Hundreds of construction workers on D.C. housing department projects may have been underpaid between 1975 and 1980 in violation of a law that requires workers on federally funded projects to be paid a "prevailing wage" generally higher than nonunion contractors pay.

City housing department chief Robert L. Moore said a city audit of payrolls for that period raised questions about whether workers had been properly paid in 5 percent of the cases. He said it was not clear how many workers were underpaid or by how much.The recently completed, year-long audit examined contracts for hundreds of millions of dollars in the construction and rehabilitation of thousands of low-income housing units.

Federal sources said the problem is far more extensive than Moore indicated, and that underpayments were probably made on most contracts during the period. A spokesman for the U.S. Labor Department, which administers the law, said there is no penalty for failing to meet the standards of the law..

"There's no one to enforce the thing," said Robert S. Parker, secretary-treasurer of the Washington Building and Construction Trades Council, which represents Washington area trade unions. "Hundreds have been underpaid. I begged Mayor Marion Barry to work harder in that compliance area." The council has endorsed Patricia Harris in the mayoral race.

Moore said that before he took office in 1979 there was no monitoring of contracts for compliance with federal pay guidelines and that he has established a contract compliance division to audit and review all contracts.

Although Moore said that the record-keeping problems occurred prior to his taking office, federal sources said the record-keeping problems continue, and that many workers are being underpaid on current housing department projects.

Federal sources said the city is having difficulty detailing the violations because the housing department never enforced a requirement that contractors turn in payroll information and other documents regularly. In many cases, the sources said, the city wrote contracts that failed to enumerate the federal wage requirements contractors were supposed to follow.

Moore said his department is advertising on the radio in an effort to find construction workers who may have been underpaid. The radio spots ask workers who think they are entitled to further compensation to call 535-1245, the housing department's contract compliance division. The number was "not in service" when a reporter called it yesterday, but city officials said it should be in service soon.

The 50-year-old federal law, called the Davis-Bacon Act, requires contractors to pay workers more than they ordinarily might -- frequently top union scale -- on any project in which federal funds are involved. The Reagan administration, claiming the law adds $600 million a year to federal building costs, has written new rules to gut it. On July 22, a federal judge halted implementation of the new rules pending further hearings.

The law was originally designed to block the use of cheap, presumably unskilled labor on federal projects by unscrupulous contractors.

Moore estimated that the Davis-Bacon requirements add $7 to $10 million to his annual capital project costs of roughly $100 million. Virtually all of the department's building and rehabilitation projects involve some sort of federal funding and are therefore subject to the Davis-Bacon requirements, he said.

"It pushes the costs of everything up," Moore said. "A laborer on a private job probably makes $10 an hour. If he works for the federal government or on a federally funded project he makes $12."

According to Moore, there are enormous difficulties in monitoring contractor compliance with Davis-Bacon requirements because of the complexity of the rules. For example, a laborer working on a house might be entitled to $8 an hour but that might jump to $10 an hour if he were working on a structure higher than two stories. Since contractors often move their workers around from project to project, compliance monitoring can be nearly impossible, he said.

Another difficulty is that wages are set under the law for each category of worker, and it is difficult to establish when contractors pay the low laborer's rate and then have their workers do other categories of work, such as carpentry, which are supposed to be higher paid.

Moore said that not all contractors who may not have adhered to the standards of the law were doing so deliberately. He said some were simply confused.