A freshly combative President Reagan today hit back at critics of his defense spending program, charging that they would risk the nation's survival at a time the Soviet Union is vastly increasing its own military capabilities.

"As much as I detest the idea of deficits, as president I must accept a large deficit if that is what it takes to buy peace for the rest of the century," Reagan said, also tying the deficit to national defense at a fund-raiser for Sen. Harrison H. Schmitt (R-N.M.).

The speech was one of two today in which the president once again indicated that he will not back down from his insistence on a record military spending increase and a 10 percent income tax cut this year.

The two have driven up the estimated deficit despite new domestic spending cuts Reagan also has proposed. Estimates of a deficit in excess of $100 billion have led to a variety of alternative proposals from members of Congress in both parties.

Reagan criticized all of these. "You've been hearing a lot about so-called alternatives," he said. "Many of these are not genuine budget alternatives at all, but political documents designed for saving certain legislators' political hides rather than saving the economy."

Before stopping here the president, who was en route to a vacation in California, also stopped in Cheyenne for a fund-raiser for Sen. Malcolm Wallop (R-Wyo.). His theme both places was that it would be dangerous to retreat even marginally from the 18 percent increase he has proposed in the military budget.

"We dare not reduce our defense budget," Reagan said in Cheyenne. "The bulk of the increase is not going for fancy new planes or elaborate weapon systems. Most of the money is for basic essentials now in dangerously short supply. It's going to go for manpower, maintenance and readiness.

"If we eliminated all the major weapons programs that are scheduled it would only reduce next year's deficit by $6.5 billion in our $3 trillion economy. I don't think Americans want their armed forces held together with chewing gum and baling wire, unable to move for want of spare parts," he said. "We must not resign ourselves to life as a second-rate power, tempting aggression with our weakness."

In his speeches today Reagan returned to the anti-Washington theme that was a dominant feature of his political speeches in years past. He said in Cheyenne that "Washington, as usual, seems paralyzed by hand-wringers," and joked, "You don't have to spend much time in Washington to appreciate the prophetic vision of the man who designed all the streets going around in circles."

Reagan was cheered by large partisan audiences in both appearances, but was met here also by about 1,000 demonstrators, lining the streets and waving placards protesting various domestic and foreign policies.

Reagan dismissed the argument that he and the Pentagon have exaggerated Soviet military strength.

"This is one subject on which the man holding the job I hold is practically the only one who has all the facts with regard to our national security," he said.

But even in Wyoming, where Reagan got 63 percent of the vote in the 1980 election, not all Republican office holders agreed with him.

Speaking to reporters aboard Air Force One en route to Cheyenne, Sen. Alan K. Simpson (R-Wyo.) said that he favors reductions in defense procurement as one way of reducing the anticipated $100 billion-plus deficit of the Reagan budget.

"Deficits do count," Simpson said. He did not specify how much should be cut from the military budget, but said, "We've got to protect against every branch of service having their own 'Star Wars' concept."

Wallop, however, said he doubted that very much could or would be cut from the defense budget.

Reagan's week-long trip will mix a little politicking with a lot of vacation.

He is scheduled to speak Wednesday in Los Angeles in behalf of his "revised federalism" program and spend the rest of the week at his secluded mountain-top retreat, Rancho del Cielo, north of Santa Barbara.