The leaders of Western Europe, Canada and Japan will come to the seven-nation economic summit at Williamsburg next weekend preoccupied by domestic politics, lingering differences with the Reagan administration over dealing with the Soviet Union and a desire for progress in arms control negotiations.

But significant changes over the past year suggest that the political agenda at Williamsburg, which will be dominated by East-West trade, arms control and the Middle East, is not likely to produce the kind of explosions that divided the western alliance during the Versailles conference last June.

National elections in West Germany that brought Christian Democratic Chancellor Helmut Kohl to power, a series of confidential agreements on tightening controls on the export of high technology to the Soviet Bloc, and a general decline in Western Europe's trade with the East have all helped lower American-European tensions on the trade issue, interviews in Europe in recent months and dispatches from Washington Post correspondents in Bonn, London and Paris indicate.

Pushing his argument that economic pressure will greatly weaken Soviet military capability, President Reagan imposed sanctions against companies operating in Europe shortly after the Versailles meeting as a way of discouraging the construction of a natural gas pipeline from the Soviet Union to Western Europe. The sanctions, generally viewed as ineffective, were lifted in November.

Kohl appears to have played a pivotal role in shifting perceptions on East-West trade by blurring the ideological emphasis that his Social Democratic predecessors put on that issue and stressing instead practical considerations that appeal to pragmatists in the Reagan administration.

"The difference is that the Social Democrats signed the gas deal with the Russians because they wanted detente," explains Volker Ruhe, a close political associate of Kohl. "They thought more trade meant more detente. We will continue the gas deal not because we want detente but because we want the gas."

Acknowledging that "the practical results will be about the same," Ruhe adds: "The Christian Democrats will stick to market conditions in dealing with the East. And we will work to overcome problems with the Reagan administration, not to emphasize them."

West Germany remains the Soviet Union's most important trading partner in Western Europe. Although only 2.6 percent of West Germany's exports go to the Soviet Union, the exports come from labor-intensive sections of the economy, with more than 100,000 jobs said to be dependent on these transactions.

But surging U.S. grain sales to the Soviet Union have pushed West Germany down to the number three spot worldwide in sending goods to the Russians, behind the United States and Japan. This change provides the Europeans with considerable ammunition for Williamsburg if Reagan returns to the attack despite private American assurances that he will not do so.

Britain's Prime Minister Margaret Thatcher is expected to point out that while U.S., West German, Italian and Japanese exports to the Soviet Union grew in 1982, the British figure dropped by 14 percent, creating a heavy British trade deficit with the Russians.

A central point of discussion at the summit will be the Reagan administration's l8-month-old effort to tighten restrictions on the export of technology to the Soviet Bloc. Under a confidential accord reached in January 1982, the Europeans agreed to strengthen controls on "peak technology" in return for what they took to be a Reagan administration pledge to allow the western alliance's coordinating committee on exports, known as COCOM, to begin removing older items from the prohibited list.

France in particular has complained that the United States has been delaying approval for telecommunications and computer technology that the French argue is outmoded and can be easily obtained elsewhere.

British and West German politicians also feel that Washington is somewhat insensitive to the political and economic problems they face at home on this issue.

"There is general agreement on principles," Michael Heseltine, the British defense minister, said. "But it always comes down to a question of whether you export a particular item and the effects of that. It often has to come back to the jobs and votes equation. Then, the theory of the dialogue doesn't usually stand up to the need to do some business."

Domestic politics are paramount considerations for Thatcher and Japanese Prime Minister Yasuhiro Nakasone, who face national elections this year, and for France's President Francois Mitterrand. Italy also has a national election next month.

Thatcher, whose Tory party is expected to win the June 9 election, will fly to Williamsburg on Saturday and return on Sunday to resume campaigning, leaving Foreign Secretary Francis Pym and Sir Geoffrey Howe, the chancellor of the exchequer, to attend the final sessions. Her appearance at Williamsburg is apparently seen as a political plus in the campaign.

Mitterrand, who watched with dismay and irritation as the agreements reached at Versailles fell apart within days, has stridently attacked U.S. monetary policy in the past two weeks in an apparent effort to rally domestic support for his embattled Socialist government. But he has canceled several American interviews that had been scheduled in what may be an indication of a desire not to take the argument to Reagan's home ground and impair U.S.-French relations.

Kohl's aides report that he will support American efforts to get a declaration of support for the deployment of Pershing II and ground-launched cruise missiles in Western Europe beginning in December. But they caution that the German leader will also want the declaration to emphasize that there is still an opportunity to get an agreement with the Soviet Union in negotiations in Geneva that would make the deployment unnecessary.

The Europeans are also expected to be sympathetic to a planned American appeal to support formally the Lebanese-Israeli troop withdrawal agreement negotiated by Secretary of State George P. Shultz. Syria has refused to participate in the withdrawal called for in the agreement, and a declaration could pressure other Arab states to support the Lebanese position.