WASHINGTON — The words were tucked deep into the sprawling text of President Barack Obama’s signature health-care overhaul. Under the headline, “Protection of Second Amendment Gun Rights,” was a brief provision restricting the ability of doctors to gather data about their patients’ gun use — a largely overlooked but significant challenge to a movement in American medicine to treat firearms as a matter of public health.

The language, pushed by the National Rifle Association in the final weeks of the 2010 debate over health care and discovered only in recent days by some lawmakers and medical groups, is drawing criticism in the wake of this month’s massacre of 20 children and six educators in Newtown, Conn. Some public health advocates, worried that the measure will hinder research and medical care, are calling on the White House to amend the language as it prepares to launch a gun-control initiative in January.

NRA officials say they requested the provision out of concern that insurance companies could use such data to raise premiums on gun owners. The measure’s supporters in the Senate say they did not intend to interfere with the work of doctors or researchers.

But physician groups and researchers see the provision as part of a decades-long strategy by the gun lobby to choke off federal support for studies into firearms injuries, which may soon overtake motor vehicle accidents as a leading cause of violent deaths in the United States.

The research restrictions began in the 1990s, when the NRA urged Congress to cut funding for the Centers for Disease Control and Prevention’s division that studied firearms violence. In 1996, Congress sharply limited the agency’s ability to fund that type of research.

More limits came last year in a spending bill setting restrictions on the National Institutes of Health after complaints from gun rights advocates about an NIH-backed study drawing links between alcoholism and gun violence. The provision, added by Rep. Denny Rehberg, R-Mont., prohibits the NIH from spending money to “advocate or promote gun control” — language that researchers say does not explicitly forbid studies but sends a signal to federal research agencies to steer clear of the topic.

The NRA push has extended into state capitals, as well, with Florida lawmakers last year crafting a plan to impose jail time on doctors for inquiring about their patients’ gun ownership. Gov. Rick Scott, R, signed a scaled-back version of the proposal requiring health-care workers to “refrain” from asking patients about their ownership or possession of firearms unless the providers believe “in good faith” that such information would be relevant. A federal judge this year declared the law unconstitutional and blocked its enforcement, but the ruling was appealed by the state and is under review.

Physician groups and public health advocates say the cumulative effect of these restrictions undercuts the ability of the White House and lawmakers to make the case for new laws, such as an assault weapons ban, in the face of opponents who argue that there’s no evidence that such measures are effective. Advocates for regulating guns lament that reliable data are limited in part because physicians and health researchers who could track these patterns are being inhibited.

“This illustrates the fact that the NRA has insinuated themselves into the small crevasses of anything they can to do anything in their power to prohibit sensible gun-safety measures,” said Denise Dowd, an emergency care physician at a Kansas City, Mo., children’s hospital and an adviser on firearms issues to the American Academy of Pediatrics. Dowd called the provision in the health-care bill “pretty outrageous,” saying it risked creating a sense among doctors that “this is dangerous information to collect.”

“We ask our patients about many things, not because we’re anti-gun, but because we have an obligation and an ethical duty to keep the kids safe,” she said.

The pediatricians group last week submitted a strongly-worded letter to the Obama administration saying that pediatric advocates “vehemently reject” the gun provision in the health-care law. The group notes that the provision runs counter to guidelines included in other sections of the legislation that ask family doctors and pediatricians to inquire about the presence of guns in patients’ homes, along with other potential dangers, such as mold, lead, cigarette smoke and a lack of smoke detectors.

In a separate letter sent last week to Vice President Joe Biden, who is heading Obama’s post-Newtown gun-control efforts, a coalition of child advocacy groups called on the administration to “renew efforts to apply science to gun safety,” demanding that Congress “immediately reverse all existing statutory bans on firearm-related research and to embark on a wide-ranging effort to fund effective gun-related research, including the collection and publication of data on gun violence.”

A spokesman for the NRA, Andrew Arulanandam, defended the restrictions on research dating to the 1990s, saying the “so-called studies were an effort to push a political agenda” with taxpayer dollars.

On the provision added to the Obama health-care overhaul, Arulanandam said the group requested the language in response to concerns that insurance carriers might use data collected as part of the law to “discriminate” against gun owners. The NRA “worked with people on the Hill and members of Congress” to ensure the provision was included in the final legislation, he said.

The provision was backed by several Democratic and Republican senators and added by Majority Leader Harry Reid, D-Nev., an NRA ally who was facing the prospect of a difficult reelection campaign in 2010.

Adam Jentleson, Reid’s spokesman, said the senator never discussed the matter with the NRA. Reid “did not think it changed gun laws in any way,” Jentleson said. Instead, Reid and others saw the provision as necessary to dispel “myths” about the health-care bill that threatened to rile up opposition, including speculation that the law would allow the Obama administration to compile a database of gun owners.

The provision says that “wellness and prevention” portions of the health-care law “may not require the disclosure or collection of any information” relating to the “presence or storage of a lawfully-possessed firearm or ammunition in the residence or on the property.” Further, the measure says the law cannot be used to “maintain records of individual ownership or possession of a firearm or ammunition.” It adds that the price of health coverage may not be affected by the ownership, possession or use of guns.

Once the section was added to the bill, the NRA withheld opposition and remained neutral. Later that year, the group decided to remain on the sidelines in Reid’s reelection campaign despite criticizing him for supporting Obama’s Supreme Court nominees.

The deal to add gun language to the health-care bill was struck so quietly that several top officials in the Obama administration and in Congress had no idea the passages had been added until approached by The Washington Post last week.

A White House official, who spoke only on the condition of anonymity, said the provision was “added into the health-care bill on the Senate floor.” For explanation on what happened, the official added, “I’d send you to the Hill.”

Sen. Al Franken, D-Minn., who sits on the Senate health committee, said he was aware of the late addition and found it “objectionable.” But, he said, “it’s helpful to remember that we were in the position of having to get 60 votes from 60 senators. And as a result, some things ended up in the bill for reasons I was not privy to and were certainly not to my liking.”

Some public health advocates and gun control proponents, though, worry that the legislative compromise erected a barrier to the type of research that could prove vital in the post-Newtown policy debate.

“Gun use and gun violence is a public health issue and it should not be out of bounds to ask questions about it,” said David Satcher, a former surgeon general under President Bill Clinton, who headed the CDC in the 1990s when the NRA began to challenge gun research. “Privacy needs to be protected, but it’s important that this kind of data be gathered.”

During Obama’s first term, he received poor grades from gun control advocates for signing bills that allowed people to carry concealed weapons in national parks and in checked luggage on Amtrak trains while not pursuing additional laws to curb violence. But the health-care provision limiting the questions doctors can ask and the restriction on NIH research in legislation he signed may prove to be a more enduring concern for gun control proponents.

“It’s a problem when you don’t have access to a high-quality stream of robust, effective research,” said Arthur Kellermann, an emergency room doctor and public health advocate who published studies in the 1980s that found elevated risks of death or injury associated with gun ownership. “And it’s an even bigger problem when you gag physicians in order to keep them from talking to their patients.”

From 1986 to 1996, the CDC sponsored peer-reviewed research into the underlying causes of gun violence. Among the findings: People who kept guns in their homes for self-defense did not gain protection. Instead, according to research published in the New England Journal of Medicine, residents in homes with a gun faced a 2.7-fold greater risk of homicide and a 4.8-fold greater risk of suicide compared to those in similar homes without guns.

The findings drew criticism from gun advocates. They pointed in part to studies by economist John Lott, who argues that people are safer when law-abiding people carry weapons and that research by Kellermann and others fails to account for other factors contributing to elevated homicide and suicide rates.

Still, the findings about gun violence led to greater interest in firearms research in an academic field that had focused largely on motor vehicle safety and tobacco. The studies struck at the heart of the argument long made by gun rights proponents that gun ownership by law-abiding people enhances safety. As recently as this month, following the Newtown shootings, the NRA’s executive vice president, Wayne LaPierre, argued that “the only thing that stops a bad guy with a gun is a good guy with a gun.”

In 1996, the NRA, arguing that such studies were biased and politically motivated, moved to undermine them.

Lobbyists for the gun industry worked with Rep. Jay Dickey, R-Ark., to redirect $2.6 million in CDC funds that had been designated for research into firearms safety. The move, which Dickey would later come to regret, unnerved scientists at the CDC and across the country.

Richard Feldman, who has had top positions in pro-gun organizations, said there was a deliberate effort to counter the work of many of these public health advocates, who he said had mistakenly begun to see guns as a pathogen. “The gun community was very upset that federal tax dollars were being used by the public health community to politicize the issue,” Feldman said. Although he has criticized the NRA recently, he concurs with the group’s decision to block funding for this kind of research. “Knowing how it could be and likely would be misused at some date, the prohibition seems quite prudent,” he said.

The NRA’s determined opposition to such research has had a visible effect on academic experts such as Garen Wintemute, who chairs the Violence Prevention Research Program at the University of California at Davis. He said that efforts to prevent gun violence have been “seriously affected by the lack of support for research, which gathers the evidence on which prevention is based.”

The lack of data on guns contrasts with the wealth of information collected about autos and roads, Wintemute noted. Research funded by the National Highway Traffic Safety Administration and its $63 million annual budget, for instance, has led to constant safety improvements. Yet gun deaths, which top 31,000 annually, may exceed automobile deaths this year for the first time, Wintemute said.

There are still pockets of support for studying gun-related injuries, such as the National Institute of Justice, a research agency within the Justice Department, and in research supported by universities and a few private foundations. But with few federal dollars, researchers say, the vast majority of financing has dried up.

“It was simply impossible to get the funding to do challenging studies” in recent years, Kellermann said.

A rare spirit of cooperation among former adversaries in the research debate emerged in the days following the July movie theater massacre in Aurora, Colo.

Dickey, retired from Congress, teamed with Mark Rosenberg, who headed the CDC’s National Center for Injury Prevention and Control in the 1990s when the NRA challenged the center’s work on gun violence, to write an op-ed article calling for new spending on scientific research of the sort Dickey had blocked in the past.

“We were on opposite sides of the heated battle 16 years ago, but we are in strong agreement now that scientific research should be conducted into preventing firearm injuries and that ways to prevent firearm deaths can be found without encroaching on the rights of legitimate gun owners,” the two wrote this summer in The Washington Post, calling for federal investments like those made to reduce deaths associated with automobiles, tobacco, and HIV-AIDs.

“Most politicians fear talking about guns almost as much as they would being confronted by one, but these fears are senseless,” they wrote. “We must learn what we can do to save lives. It is like the answer to the question ‘When is the best time to plant a tree?’ The best time to start was 20 years ago; the second-best time is now.”