When Soviet leader Mikhail Gorbachev sits down for breakfast with Vice President Bush on Thursday morning, he will find an aspiring American political leader who has some different ideas about U.S.-Soviet relations than the president he has loyally served for the past seven years.

Gorbachev also will find American citizens from Iowa and New Hampshire in the vice president's breakfast delegation -- a reminder of Bush's current preoccupation, the presidential campaign.

The breakfast at the Soviet Embassy is the centerpiece of the vice president's participation in a summit that could produce important political gains while also offering insights into how he would deal with the Soviets if elected next year.

Although it was not widely recognized in the years that Bush served in Reagan's shadow, the vice president holds much more traditional views about dealing with the Soviets than did Reagan when he came to office, and is described by aides as eager to proceed further with negotiations if he is elected president.

"He was always in favor of getting on with the process," said Daniel J. Murphy, a retired Navy admiral who served as the vice president's chief of staff in the first term. "This didn't mean giving the farm away, but getting on with it . . . . It runs right through his

character. Problems ought to be solved . . . . "

Bush has stressed negotiations in his current campaign. In an address at the Naval Academy last spring, he said, "We need to talk to the Soviets. This is a nuclear age, which means it's simply not sane to sit in stony silence at bomb's length from powerful adversaries."

In other speeches, Bush has said he would bargain with Moscow on banning chemical and biological weapons, on reducing strategic nuclear forces, and on redressing the conventional force imbalance in Europe.

This has set Bush apart from the other Republican contenders, who have called attention to past Soviet treaty violations and warned of future ones. His leading rival, Senate Minority Leader Robert J. Dole (R-Kan.), may back the intermediate-range nuclear forces (INF) treaty that Reagan and Gorbachev are to sign on Tuesday but also seek changes. The other Republican candidates all oppose the treaty.

In a thorough mix of domestic politics and diplomacy, Bush has turned the medium-range missile treaty into something of a campaign doctrine. He made a whirlwind tour of European capitals, at taxpayer expense, just before his formal announcement, to highlight his association with the pact, although the trip had almost nothing to do with the negotiations. He has stressed his support repeatedly since then, and last week in Iowa he all but discarded talk of other issues, such as education and the budget, to stump for the pact.

"This is the most important matter in the Reagan presidency, and the only Republican supporting him is George Bush," said campaign manager Lee Atwater.

Bush strategists also see the summit and the treaty as enhancing the "stature advantage" of his long experience in government and diplomacy. And they realize Bush will be in the limelight at a time when the presidential campaign is in a lull. "To the degree the country is focused on this set of issues, it's an advantage to us," said Bush pollster Robert Teeter.

For Bush, the main event is Thursday's breakfast. Sources said the event involves about 25 people, divided among Soviet and American guests. Bush is inviting several Americans from around the country, including an Iowa educator, and others may be from New Hampshire, the two states with the most critical early campaign tests next year.

The vice president also plans a public role in appearing on network television interviews during the week and may deliver a speech on the summit in Iowa next Friday. Bush is invited to all the meetings with Gorbachev that are not one-on-one between Reagan and the Soviet leader, although Bush was not present last week with the president at the final preparatory meeting on arms control because he was in Iowa campaigning.

Bush has his own brief session alone with Gorbachev just before the Thursday breakfast, and the vice president is also scheduled to ride to Andrews Air Force Base with the Soviet leader and lead the departure ceremony on Thursday.

A senior adviser said Bush wants the session with Gorbachev to be a "look forward" at issues dividing the superpowers.

Bush played little or no role in the internecine arms control battles of the first and second Reagan administrations, according to a number of participants.

Several sources have suggested that Bush, in tandem with former national security adviser Robert C. McFarlane, did play a role in Reagan's decision at the end of his first term to take a more conciliatory approach to the Soviets. According to Murphy, Bush would have moved in this direction sooner. Bush "would be on the side of discussing things with the Soviet Union," Murphy said. "The president definitely is in that mode today, but he wasn't in the beginning."

McFarlane continues to advise Bush on national security matters, aides said. Other current advisers -- outside the White House -- include Richard R. Burt, now the ambassador to West Germany, and Alton G. Keel Jr., the U.S. ambassador to NATO, who returned to the United States with Bush after his recent swing through Europe.

The vice president has embraced many Reagan policies, but with some reservations and differences. Bush has strongly endorsed the "Reagan Doctrine" of supporting anticommunist forces in such places as Nicaragua and Afghanistan; advisers say Bush would certainly continue this effort. The vice president also has embraced Reagan's moral justification for the Strategic Defense Initiative, the space-based missile defense, but Bush does not advocate early deployment or huge spending increases for it. Bush has not advocated a major defense buildup from current levels.

In his announcement speech, Bush said the medium-range missile treaty was only a "prelude to serious talks on strategic arms, conventional weapons, chemical weapons, biological weapons -- all these things."

Bush, said a senior adviser, has a "willingness to engage" the Soviets, "a willingness to deal."

Staff writer T.R. Reid and researcher Michelle Hall contributed to this report.