Congressional leaders offered support to President Bush yesterday for the trade agreement that he signed at last week's summit with Soviet President Mikhail Gorbachev but warned that the treaty could face strong opposition in Congress if the Soviets do not ease their economic blockade against Lithuania.

Bush briefed the bipartisan leadership on the summit at the White House yesterday, and House Speaker Thomas S. Foley (D-Wash.) and Majority Leader Richard A. Gephardt (D-Mo.) spoke up forcefully for the trade agreement, according to officials present.

Foley told Bush that he believed it was "correct" to sign the pact and that the president had handled the issue of Baltic independence "well." Gephardt told Bush he believed that the agreement would strengthen the U.S. position with regard to the Baltics. "I think it's better for us to have the trade agreement than to have not had the trade agreement and not had any progress on Lithuania either, and I think that's what would have happened if the president had taken that very hard line," Foley said.

Even Senate Majority Leader George J. Mitchell (D-Maine), who sharply criticized Bush Monday for failing to be tougher on Gorbachev over Lithuania, was muted during the meeting.

But the leaders said later that Lithuania remained an obstacle to the treaty. "Call it linkage, or call it reality," Senate Minority Leader Robert J. Dole (R-Kan.) said. "If the Lithuania or Baltic problem is not resolved, then I think it will become a matter of great concern in the Congress."

The administration repeated yesterday that the only precondition for sending the trade agreement, and a request for favorable tariff treatment, to Congress is Soviet passage of a measure liberalizing emigration. But the Soviet legislature yesterday put off that bill. "We can't say it's a good thing," an administration official said of the delay. "But it may work to their benefit . . . . Gorbachev knows that he needs to get a dialogue going in Lithuania to ensure American support."

White House press secretary Marlin Fitzwater said Bush told congressional leaders that Gorbachev made no private assurances about Lithuania before the go-ahead decision on the trade agreement, which Gorbachev badly wanted.

Fitzwater also reported that Bush received a message from Gorbachev as his aircraft cleared U.S. airspace. "Having completed my stay in your great country, once again I wish to express my deep satisfaction with the results of my visit," it said. "The work we have done together during these days will bear good fruit."

Staff writer Ann Devroy contributed to this report.