WASHINGTON — Four and a half years ago, the Social Security Administration set out to reduce a growing backlog in appeals from sick and disabled Americans who could no longer work but were denied disability benefits.

A study due out Monday concludes that despite these efforts, and despite assertions by top agency officials that things have improved, the backlog has only grown in the past year – and a spike in new applications is threatening to swamp the system.

The review by the Transactional Records Access Clearinghouse, an independent research organization at Syracuse University, found that 735,660 appeals will be pending in the current fiscal year, up from 705,367 in fiscal 2010. Applicants waiting for their appeals to be heard will wait an average of 369 days, a big improvement from the peak of 514 days in 2008 but still more than a year, the report found.

“The question is, is the agency achieving its stated goals?” said TRAC’s co-director, David Burnham. “The answer is no.” The review analyzed data provided by the Social Security agency, Burnham said.

Social Security Commissioner Michael Astrue assailed the report as a “real disservice to disabled Americans” and Congress, whom he said will be misled by its conclusions. In the past two years, the agency has indeed struggled with a wave of new applications for disability benefits from about 200,000 people each year, he said.

But that growth should not be considered part of a backlog in processing appeals, which have edged closer to Social Security’s goal of 270 days to resolve, Astrue said.

“No matter what we do, we’re always going to have a certain number of cases in the queue,” he said. “We’ve made nothing but steady progress for four straight years.” He called the report “research fraud” for implying that new applicants become part of the backlog.

“If you filed for disability tomorrow, would you be backlogged in a day?” Astrue said.

The dispute comes as the aging of the baby-boom generation and high unemployment are prompting more people to apply for benefits. Many Americans who had worked despite their disability got laid off and applied for help.

The Social Security Administration is using teleconferences and other innovations to speed up hearings. In recent years, Congress provided money to hire nearly 500 administrative-law judges and 1,500 support staffers to process appeals. Most applicants whose cases are turned down appeal the denials to these judges, who have the power to force the agency to grant benefits.

The agency has worked for a decade to improve how it evaluates applications, but the backlog has persisted, drawing attention from congressional watchdogs.

Astrue made computer upgrades to sift through claims and identify clearly disabled applicants to improve the initial screening process. Two-thirds of those who appeal an initial rejection eventually win benefits.

The agency’s rules are strict: To get disability benefits, applicants must prove that they can’t do work of any kind. That’s one reason getting benefits is complicated and, for most people, takes multiple appeals. Payroll taxes support the system.

Astrue said about 214,000 Americans have been waiting more than 270 days to have their appeals resolved, while more than 500,000 wait less than 270 days. “If it’s less than 270 days, it’s normal processing,” he said. “If it’s more, we consider that bad, and we’re trying to stop that.”

He said advocates for the disabled pushed for the 270-day target to ensure that applicants have time to find attorneys and advocates to help them through the appeals process.

With budget cuts this year and more expected in the next fiscal year, Astrue said he does not expect to hire more administrative judges to handle appeals.