The idea of finding some compromise on the contentious issue of military aid to the Nicaraguan contras lost ground yesterday at the White House and on Capitol Hill.

At the same time, the top U.S. military officer in Central America, Gen. John R. Galvin, said yesterday that congressional refusal to provide military aid would not doom the Nicaraguan rebels. "They're not going to collapse if we don't give them something," said Galvin, commander of the U.S. Southern Command in Panama, in an interview at The Washington Post.

Last week, White House communications director Patrick J. Buchanan said, "If we don't get that assistance to the contras, they'll be defeated."

In an interview with out-of-town journalists, President Reagan said he would reject any effort to delay or reduce the aid request, which consists of $70 million in military assistance and $30 million in nonlethal "humanitarian" aid.

Reagan specifically rebuffed a proposal by Sen. Jim Sasser (D-Tenn.) that Congress approve the aid but withhold its use for six months while efforts are made to arrange peace talks between the Nicaraguan government and the rebels.

"In the last few days here in Washington there has been talk of compromise on this issue: smaller amounts of aid, delay in providing it, restrictions on the uses to which it could be put, all the usual temporizing and quibbles," the president said.

He said he objected to the delay in the Sasser plan, and to its provision that Congress would have to vote a second time before the aid could be used. "I don't think that would be a compromise that I could listen to at all," he said.

On Capitol Hill, an administration suggestion for a "nonlegislative compromise" to the contra aid issue appeared to generate little enthusiasm.

White House officials have suggested that Reagan could promise in a letter to Congress not to send the military aid to the rebels for a specific period of time -- probably 60 or 75 days -- while U.S. and Latin American diplomats try to bring the Sandinista government and the contras to the bargaining table. After this delay the aid would be delivered, whether or not negotiations had begun.

Sasser rejected this proposal, and charged that the administration broke a similar promise last year to seek a diplomatic solution in return for congressional approval of $27 million in humanitarian aid to the rebels. Sasser said, "The administration doesn't have a lot of credibility."

One reason for the hardening attitude at the White House appeared to be the complaints from House Republican leaders that talk of compromise was undermining their effort to win passage of Reagan's aid request.

House Minority Leader Robert H. Michel (R-Ill.) described himself as "floored" and "distressed" by the compromise suggestions that have been floated in recent days.

The Democratic-controlled House is scheduled to vote on the contra aid request next Wednesday, and Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) said that as of last week the proposal would have lost by about 25 votes. A House aide, who dismissed Reagan's claim to have "turned the tide" on the issue as an attempt to "create illusions," said there had been no erosion in the Democratic opposition to the aid request.

The administration stands a better chance in the Republican-controlled Senate, but even here the prospects for passage were described by Sen. David F. Durenberger (R-Minn.) as "at best 50-50."

Yesterday, four senators -- Appropriations Committee Chairman Mark O. Hatfield (R-Ore.) and Sens. Patrick J. Leahy (D-Vt.), Tom Harkin (D-Iowa) and Paul Simon (D-Ill.) -- announced their opposition to the aid package, saying the $100 million could be better spent on a variety of domestic needs, including student loans, aid to the elderly poor and farm programs.

Their opposition was one indication of how the current budget climate and concern over the federal deficit appears to be working against the contra aid request. In the interview with reporters, Reagan conceded that White House polls show the public has not lined up behind the request.

Gen. Galvin said yesterday he would like the U.S. military to play a modest role in advising and training the rebels battling the Sandinista government in Nicaragua.

Galvin said he believes the contras have improved as fighters during the past year, but that they need assistance in logistics and tactics and strategy. He said the U.S. military, which until now has not been permitted to work with the CIA-trained contras, is best equipped to provide such advice.

"I'm talking about a few people," he said. "I'm not talking about U.S. involvement in Nicaragua. I'm talking about advice and just passing on some ideas, and maybe doing some training somewhere."