Vice President Bush, saying that the nation is in a period of budgetary expansion, pledged yesterday that if elected president he would seek further increases in U.S. military spending despite seeming improvements in U.S.-Soviet relations.

Bush spoke to reporters at a breakfast less than 12 hours after seeing off Soviet leader Mikhail Gorbachev at Andrews Air Force Base. He left immediately afterward for a campaign swing in Iowa, where he picked up the endorsement of the mayor of Ames, who said he was defecting from Senate Minority Leader Robert J. Dole (R-Kan.) because of Dole's reluctance to support the Intermediate-range Nuclear Forces (INF) Treaty signed this week.

At the breakfast, Bush said he sees nothing in the international climate that would lead to substantial reductions in defense spending.

"I think it {military spending} ought to keep going, and it will, go up," Bush said. "And it should go up, but so will a lot of everything else. We're in an expanding economy; we're in expanding budgetary times."

Bush said he is "not one of those" who say that "things are better now, therefore we ought to cut defense."

Bush said that "defense has taken a hit" in recent congressional deliberations and that substantial sums may be needed in the future for conventional forces in Europe in the wake of the elimination of medium-range and shorter-range missiles by the U.S.-Soviet treaty.

On President Reagan's Strategic Defense Initiative (SDI), Bush said he would "just keep going forward" with "a full research program which includes testing." He said he had told Soviet leaders in private conversation this week that "I would treat the matter the same way" as the Reagan administration if he were elected president.

In view of this week's accommodations between Gorbachev and President Reagan, Bush said, SDI should not be the ultimate obstacle to deep cuts in U.S. and Soviet strategic offensive arms as had been widely expected before.

A greater problem for SDI, Bush suggested, is in Congress and in the presidential campaign. "That's a lot of what the election is going to be about," Bush predicted. He said he is "going to be saying, 'Hey, here's what I want: full-scale testing,' get it developed as quickly as one can."

The vice president, who had a private meeting and breakfast with Gorbachev Thursday morning and accompanied the Soviet leader on motorcades to the White House and to Andrews Air Force Base, said he found Gorbachev "a leader {and} able in almost a unique way in modern history to communicate with the West."

"It's very obvious there's something quite different stylistically" about Gorbachev, he continued. "He can be tough, he can smile {and} he can turn right around and very, very forcefully, not angrily, but forcefully make a point."

Bush brushed off charges that his decision to invite guests from Iowa and New Hampshire to his breakfast with Gorbachev was politically motivated.

"I just assume that goes with the territory . . . . {I'll} probably get a little more on that in Iowa. C'est la vie," said Bush.

Later in Iowa, he moved quickly to take advantage of his participation in the summit, telling a series of small-town audiences that he wants to be "the president that builds on" the success in signing the INF Treaty.

Bush portrayed himself as an administration insider who met privately with Gorbachev three times -- twice in limousines -- and played an active role in forwarding the cause of peace.

Bush was introduced at a local Moose lodge in Ames by Mayor Paul Goodland, who said that he had decided to switch his support from Dole to Bush because Dole was too "reluctant" in endorsing the INF Treaty.

Dole said this week he believes the treaty will be ratified in the Senate, but added that he is not ready to say whether he will vote for it.

"We recognize that Sen. Dole has not taken a politically expedient position on the INF Treaty," Katie Boyle, a campaign spokesman said in Washington. "We know in the long term people will know he did the right thing."

Dole, who was part of the congressional delegation that met with Reagan at the White House yesterday, was asked after the session whether he thought Bush had gained a political advantage from the summit.

"Being endorsed by Gorbachev?" Dole shot back.

Bush told his Iowa audiences he wanted to be the follow-on president to complete a very broad and very aggressive arms control agenda.

Staff writer Gwen Ifill in Iowa contributed to this report.