The planned construction of a new Woodrow Wilson Bridge moved a step closer yesterday when area members of Congress introduced legislation, proposed by the Clinton administration, to guarantee an additional $600 million for the $1.9 billion project.

While the plan has won unanimous support from the Washington region's delegation, it could still face a tough fight, especially in the House, where a key transportation subcommittee chairman has said he will oppose anything beyond the $900 million previously promised.

"It's going to take some dialogue and understanding," said Rep. Thomas M. Davis III (R-Va.), a chief backer of the spending plan, at a news conference yesterday attended by most members of the delegation. "It's something you really have to make the case for."

Davis, a member of the Republican leadership in the House, said he has already begun to argue that case with Rep. Thomas E. Petri (R-Wis.), chairman of the ground transportation subcommittee. Petri sharply criticized the spending proposal last month, dashing hopes that it could win swift approval. Davis said he also has spoken with Rep. Bud Shuster (R-Pa.), who could ultimately hold the key to the proposal's fate as chairman of the House Transportation and Infrastructure Committee.

Those talks coincide with efforts by the administration to secure congressional support for the plan, which involves spending $150 million a year for four years beginning in 2004. Secretary of Transportation Rodney E. Slater said last week he has begun to discuss the matter with Shuster but offered few details.

Winning funding approval from Congress is just one hurdle for the Wilson Bridge, which faces the prospect of a long delay because of a U.S. District Court ruling three months ago ordering a halt to construction pending more environmental review. U.S. transportation officials have appealed that decision.

At yesterday's highly publicized news conference, area legislators played to a pair of audiences: other members of Congress and area motorists, who face the prospect of more congestion as traffic volume continues to outstrip the capacity of the aging span, which carries Interstate 95 and the Capital Beltway over the Potomac River. Because the bridge is deteriorating, transportation engineers warn that truck traffic could be barred in 2004 unless a new span has opened.

"In my judgment, this is the most important federal project for the entire region," said Sen. Charles S. Robb (D-Va.).

While noting its regional significance, members sought to frame the issue as a matter of national priority and argued that the Wilson Bridge is unique as the country's only federally owned span.

"This is the nation's capital's bridge," said Sen. John W. Warner (R-Va.).

Members were wary of detailing their strategy for winning approval from critics, who say Virginia and Maryland should contribute more. Under the current plan, their obligation would total nearly $400 million.

But area legislators were hopeful the proposal could win the necessary consent. "We think we can move forward and work with them on this," said Rep. Albert R. Wynn (D-Md.).