Lawyers for Metro have begun negotiations over a proposed $13.5 million settlement of claims by subway construction workers who allegedly suffered job-related injuries or diseases -- a markedly lower amount than the transit authority previously indicated.

Metro officials recently urged Congress to pass legislation to block the construction workers' lawsuits, warning that the claims would cause "serious financial problems" and could delay plans for extending the rail system.

In a statement last month, Metro said the claims "could cost the authority hundreds of millions of dollars."

Congress has not adopted the legislation sought by Metro. However, Rep. Frank R. Wolf (R-Va.) proposed a bill two days ago to block the lawsuits, saying they could cost Metro billions of dollars. Sen. John W. Warner (R-Va.) proposed a similar move, citing estimates of "staggering" costs.

In a Sept. 26 letter, William F. Mulroney, a lawyer for the construction workers, offered to settle "all pending cases" for $13.5 million. Vincent H. Cohen, a lawyer representing Metro, said he had found ambiguities in the proposal and asked Mulroney for clarification.

The proposed settlement stemmed from a series of lawsuits by subway construction workers, including some who allegedly suffered lung ailments at tunnel excavation sites in the 1970s and early 1980s.

In June, the U.S. Supreme Court ruled that the transit agency may not be sued by injured construction workers. The decision was hailed as a victory by Metro officials.

However, Congress enacted legislation last month that, according to Metro and other officials, has had the effect of nullifying the court ruling and has left Metro vulnerable to suits. Metro officials now are seeking further legislation to counter the effect of the earlier measure.

Metro officials previously have said that 399 lawsuits were filed seeking awards totaling $3.5 billion.

These figures were questioned yesterday by Mulroney and Peter J. Vangsnes, another lawyer for the workers. They said only 95 to 110 suits had been filed, and described Metro's contentions as exaggerated.

Cohen acknowledged that Metro's figures may be subject to question. "The language might have been loose," he said. Cohen said he knew of about 140 lawsuits -- not 399 -- and he described the $3.5 billion total as including all claims lodged against Metro or any of the authority's subcontractors.

Mulroney and Vangsnes said many of the claims against subcontractors were recently withdrawn. In addition, they argued, initial claims in a lawsuit often are far in excess of any amount awarded by a jury.

Mulroney said the $13.5 million proposal was aimed at settling all pending suits against Metro or its subcontractors. The proposed amount may be reduced through negotiations, lawyers acknowledged.

Mulroney said an additional amount -- probably several million dollars -- would be sought for claims by about 20 other workers planning to file suits shortly. No settlement has been discussed for other claims that may be filed in the future, lawyers said.