BANGOR, Maine — A new coalition of law enforcement officials, gun violence survivors, sportsmen, gun owners and gun violence prevention advocates launched a campaign Saturday in support of a November referendum to require background checks for nearly all firearms sales in Maine.

The group, Mainers for Responsible Gun Ownership, held a gathering on Harlow Street to spread the word about the referendum, which was sponsored by South Portland residents Judi and Wayne Richardson. Their daughter, Darien Richardson, was shot with a pistol while she slept in her Portland apartment in January 2010 in a homicide case that has never been solved.

Criminal background checks are required by the federal government for gun sales at licensed gun shops and retailers in Maine, but the law has a loophole that allows private sales to go forward without them.

“That means felons, domestic abusers and other dangerous people can easily buy guns anonymously from unlicensed sellers — including at gun shows, through classified ads and from strangers they meet online — [with] no background check required, no questions asked,” the coalition’s spokesman David Farmer said in a release about the event. “The Maine Background Check Initiative would close this loophole by requiring that everyone buying a gun in Maine get the same background check, no matter where they buy it or who they buy it from.”

The referendum before voters is to make background checks a part of all gun sales in Maine with the exception of those involving family members.

The proposed Maine initiative would require all unlicensed sellers to meet the buyer and complete the sale at a licensed gun dealer, who would run a background check through the FBI’s National Instant Criminal Background Check System, which was put into place in November 1998.

People who are convicted felons, involuntarily committed to mental institutions, addicted to illegal drugs, dishonorably discharged from the military or in the country illegally are barred from owning guns.

“The background check initiative, which will be on the ballot in November, protects law-abiding gun owners while making it harder for dangerous people to get guns,” Lincoln County Sheriff Todd Brackett said in the press release.

Volunteers spent part of Saturday doing door-to-door canvasses in Damariscotta, Portland and Rockland, said Farmer.

Gatherings are planned in Eastport, Belfast, Norway and Houlton in the next week, Farmer said.

“Background checks work,” Caribou police Chief Michael Gahagan said in the released statement. “Since 1998, they have prevented more than 2.4 million felons, domestic abusers, people with severe mental illness and other dangerous people from getting guns nationwide.”

In states that already require background checks for all gun sales, “46 percent fewer women are shot to death by their partners and 48 percent fewer law enforcement officers are killed by handguns,” Gahagan said.

While the initiative will not prevent every tragedy, it will make Maine safer and save lives, Judi Richardson said in the press release.

“We cannot bring Darien back, but we are committed to doing everything possible to protect others from this pain by reducing gun violence,” she said.