Washington — The US budget impasse is severely dampening expectations for the coming economic summit at Williamsburg, Va. President Reagan has been unable to reach a budget compromise with Congress, with so much politically at stake in his own country. So how, ask some foreign leaders, can he be expected to reach concrete agreements with leaders of the other six major economic powers, in a single weekend, over such weighty matters as huge future deficits, high interest rates, or quickening the pace of world recovery?
As a result of the budget stalemate, Williamsburg participants are trying to lower expectations for anything like decisive US action on key economic issues.
''I don't think we will have a very clear signal (on Reagan deficit policy) at Williamsburg, given the budgetary calendar,'' said French Ambassador to the United States Bernard Vernier-Palliez.
US Treasury Secretary Donald Regan says much the same thing about the budget's uncertain course in Washington.
''The President will be assuring the other people at the summit that he will be working to get the United States deficits down in the out years (1985 and thereafter),'' Regan told reporters in outlining US goals for the summit. ''He feels very strongly on this subject and believes obviously that the proper way to do it is to cut spending, not to raise taxes.
''Now, as to how the President will achieve this, all he can do is to describe the political process that he's going to have to go through, which is to either work with the Congress to get it down or to veto what the Congress does - if the Congress indeed comes up with spending that's too much for him to stomach or comes up with tax increases that he doesn't like.''
But the participants do have hopes for some gains from the summit.
For President Reagan and the American team, the primary objective is to reinforce the impression of global economic recovery.
This would help Reagan at home. The President is likely to get some slight uplift in public approval from the summit, with extensive press and television coverage of his sessions with heads of state. This happened last summer after the economic summit at Versailles, when Reagan traveled to Rome, London, Berlin, and Bonn in a European tour.
But more than ceremonial fallout from Williamsburg is at stake. Reagan's recent upward lift in the polls largely reflects the public perception that the long-awaited US economic recovery has begun.
A US emphasis on indications that a world recovery is in progress could add to the gains Reagan has begun to enjoy in the polls.
Reagan's stress on recovery will, however, be tempered by concern from other quarters that the upturn be extended beyond the US to other countries, as well as by warnings that recovery could be aborted by a renewed surge in US interest rates.
''We have a good story to tell,'' Secretary Regan says. ''The worldwide recovery could get under way this year because it has already started in most industrialized countries, led by the United States.''
US interest rates have declined from around 17 percent, at the start of the Reagan administration, to just under 9 percent, Regan says. And inflation rates in the US and other major countries, with a notable exception in France, have likewise moved downward.
Other participants take issue with these assertions. The French say that real interest rates, which were 8.5 or 9 percent a year and a half ago, are now about 7 percent, which shows ''little progress.''
And the other economic powers have less prospect for unemployment relief from the purported world recovery - with more than 30 million unemployed in the Organization for Economic Cooperation and Development countries alone - than does the United States.
But none of the countries apparently is looking for a quarrel at Williamsburg. The French have backed away from an aggressive stance.
The most significant change sought by the French at Williamsburg, says Ambassador Vernier-Palliez, is to convince Western leaders ''to take notice of the importance of third-world recovery for the global recovery.''
The French are apparently satisfied they have already made their point about the need to consider another Bretton Woods-type conference on monetary system changes. Planners for the summit have proposed a study of the idea. Vernier-Palliez indicated that ''it took three years of discussion for a much easier problem'' at Bretton Woods. ''What is needed at Williamsburg is a signal that the matter is going to be taken seriously,'' Vernier-Palliez said.