A Clinton administration proposal to spend an extra $600 million on replacing the Woodrow Wilson Bridge won a warm reception from Maryland and Virginia officials yesterday but faces a more uncertain future in Congress.

The financing plan unveiled Monday could remove one of the most vexing obstacles to a new Potomac River crossing and would boost the federal contribution to $1.5 billion, requiring the states to fund the shortfall, now estimated at $400 million to $500 million. That would leave Maryland and Virginia with a far more modest burden than some federal officials previously had urged.

"We were very pleasantly surprised," said David Chapin, Maryland's assistant transportation secretary. "We were very pleased with the U.S. Department of Transportation and the administration for bringing forward this proposal."

Chapin, however, stopped short of endorsing the plan, saying that must await the return of Gov. Parris N. Glendening (D) and state Transportation Secretary John D. Porcari from overseas trips.

Officials in both states also have been reluctant to sign off on the package until they review the details, including any limitations on the timing of the payments or on which state accounts could be used for the funds.

Virginia Transportation Secretary Shirley Ybarra said she discussed the plan Monday evening with Gov. James S. Gilmore III (R), who was upbeat but eager to review the specifics. Ybarra said both governors have said previously that they would be willing to jointly contribute at least $350 million toward replacing the aging span.

"We're very encouraged," she said. "We've got to get it through Congress."

That could prove yet another test for the Wilson Bridge project, which already faces the prospect of a long delay because of a U.S. District Court ruling two months ago ordering a halt to construction until more environmental review is done. U.S. transportation officials appealed that decision Monday as part of a two-front strategy to eliminate both legal and financial impediments to replacing the region's premier river crossing.

The administration's proposal to Congress to spend $150 million a year for four years starting in 2004 is unusual because it is a request to start spending after the expiration of the current six-year multibillion-dollar transportation program.

"It's not something that's done every day, but it's not a total exception to the rules," said Jack Basso, assistant U.S. transportation secretary for budget and programs. He said such advance authorization is common in defense spending but not domestic.

The stiffest resistance may come from the House Transportation and Infrastructure Committee, which has signaled it has little interest in supplementing the initial $900 million pledged last year by Congress for the Wilson Bridge. Basso declined to discuss any conversations he has had with committee Chairman Bud Shuster (R-Pa.).

"We would hope Congress will work closely with us to provide this funding. . . . Very soon we hope to send up legislation to the committee," Basso said. He said that could happen within five days.

Although the Washington region's congressional delegation has unanimously applauded the administration's financing plan, members acknowledged that passage is not assured. Rep. Thomas M. Davis III (R-Va.), a key member of the Republican leadership in the House, said winning the extra $600 million is not "a slam-dunk."

Rep. Frank R. Wolf (R-Va.) said, "I'm hopeful it can be [approved], but we'll have to see how this thing will move."

On the Senate side, prospects are bright, according to Sen. John W. Warner (R-Va.). "I have a level of confidence . . . we can present a convincing argument to the Senate," he said. "If that bridge were to fail from the standpoint of safety, it would be paralytic to the operation of government in the nation's capital."

The fate of the financing package also is of great interest to Alexandria activists, who are battling to scale back the plans to erect a 12-lane bridge. They prefer a less expensive 10-lane structure.

"We're still trying to figure out how the $600 million will fly with Congress," said Judy McVay, co-chair of the Coalition for a Sensible Bridge. "That's a lot of money for the feds to put into one project."