WASHINGTON — Seeking union support, Senator Clinton is among several Democratic presidential contenders calling for increased enforcement of a 76-year-old labor law that requires the payment of prevailing wages on public projects.

Speaking at a candidate forum yesterday, Mrs. Clinton lambasted the Bush administration for suspending the Davis-Bacon Act in the wake of Hurricane Katrina in 2005 and vowed to protect and expand the law if elected president. The bill was first enacted in the midst of the Great Depression in 1931, and labor unions have fought to keep it on the books over criticism that it is too expensive to taxpayers and overly regulatory. It is named for a former Republican senator and labor secretary, James Davis, and a Republican congressman from Long Island, Robert Bacon.

“We’re going to stand with Davis-Bacon, because our workers deserve better wages, and nothing less,” Mrs. Clinton told about 2,500 members of the Building and Construction Trades Department, an affiliate of the AFL-CIO. The coalition of unions heard speeches from seven Democratic hopefuls yesterday.

Citing the administration’s action days after Katrina, Mrs. Clinton said President Bush “just doesn’t get it” when it comes to Davis-Bacon, a critique that was echoed by several candidates, including a chief Clinton rival, Senator Obama of Illinois.

Following an outcry by unions and many Democrats, the administration reinstated the law weeks later. A White House spokesman, Blair Jones, said yesterday that the temporary measure was “part of an administration-wide effort to remove as many barriers as possible to aid the recovery efforts in the impacted areas” of the hurricane. “The administration supports maintaining the act in its current form,” he said.

As a step toward increased enforcement of Davis-Bacon, Mrs. Clinton said yesterday that she would introduce a bill that would give unions access to employer payroll records, so they could see if they were paying prevailing wages. Although the issue has fallen largely along party lines in recent years, she sought to cast it as nonpartisan. “This is not a Democratic or a Republican issue. It is a fundamental workers’ rights issue,” she said.

Opponents of the measure often cite its history, saying its passage in Congress was part of an effort by white-dominated unions to keep jobs from going to lower-paid, non-unionized black workers. “Frankly, it was almost a viciously racist piece of legislation,” an economist at the conservative American Enterprise Institute, Richard Vedder, said. Mr. Vedder said it was “ironic” that Democrats have taken to defend the act, given the party’s deep support among black voters.

The law is outdated, he said, and it contributes to higher construction costs and budget deficits. “Trying to enforce higher wages to protect union workers strikes me as not in the national interest,” Mr. Vedder said.

Yesterday was the second straight day that Mrs. Clinton and her top Democratic rivals, Mr. Obama and John Edwards, addressed large union crowds. The president of the Building and Construction Trades Department, Edward Sullivan, said the organization, which represents more than 2 million union members, would likely make an endorsement later this year.

Also yesterday, Mrs. Clinton received the endorsements of the National Organization for Women and the retired tennis star, Billie Jean King.