Republican presidential candidate Alexander M. Haig Jr. yesterday criticized his rivals for neither understanding the nation's problems nor offering realistic solutions, but reserved equally tough criticism for President Reagan.

Haig told Washington Post editors and reporters that Reagan's tax cuts and spending policies, particularly his defense buildup, are responsible for the enormous federal budget and foreign trade deficits and said that the defense buildup in the first years of the Reagan administration was wasteful and possibly counterproductive.

"Our most important problem, the deficit and our debtor nation status, dwarfs everything else," Haig said. "It overwhelms everything. And we have problem areas such as the rust-bucket industries and the agriculture sector."

The budget deficit, Haig said, is the result of the tax cuts and the Federal Reserve Board's tightening of the money supply and raising interest rates to fight inflation.

"We had two directly contradictory economic theories, one -- the tax cuts -- a growth theory, the other a restraint theory," he said. "We threw the economic engine into first gear and reverse at the same time and the grinding you heard was the mounting federal deficit."

He said the defense spending surge in 1981, 1982 and 1983 was "excessive."

"You can't spend that much money in a coherent way, and {Defense Secretary Caspar W.} Weinberger failed to put forth a coherent strategic cost estimate to flesh out what was needed," Haig said.

Because of this and the budget deficit, Haig said that all the other presidential candidates are looking at the defense budget as a primary area for spending cuts.

"This administration threatens in eight years to be the largest defense spender and the largest defense cutter simultaneously, and that's the worst kind of defense policy there is," he said. "Most of the major procurements are on five- or 10-year programs, and terminating those is the most expensive way to cut. It leaves a narrow window of expungeable spending on personnel, readiness and other vital areas."

Haig also faulted the administration's policy in Nicaragua and said that the United States missed a diplomatic opportunity to work out a broad solution with the Soviet Union and Cuba in 1981 and 1982.

"We should have made a broad approach, gone to the source, to the Soviet Union and Havana, to get them out of Nicaragua," he said.

The United States could have offered Cuba incentives through an altered relationship with the United States, he said.

"You have to have some sort of understandings in a situation like that," he added.

Haig also charged that the administration ignored his proposal when he was secretary of state that the United States try to bring an early end to the Iran-Iraq war.

"I sent a memo that this is a strange war in which we don't want a winner, and I suggested that we launch a United Nations effort to bring it to a conclusion without a victory for either side," he said. "It sat on {former national security adviser} Bill Clark's desk for months."

Haig credited the administration with returning the nation's focus to "traditional values and institutions" and reliance on "free enterprise and the private sector" rather than centralized federal programs.

"It's important that we feel good about ourselves, but now it's time to be good," he said. "It's time to go from a feel-good to a be-good society."

He predicted that Jesse L. Jackson will win the southern regional "Super Tuesday" primary with 25 percent to 30 percent of the Democratic vote and that white Democrats will turn to New York Gov. Mario M. Cuomo, who he says is "clearly going to run."

"Our two front-runners {Vice President Bush and Sen. Robert J. Dole (R-Kan.)} were 20 or 30 points in the polls behind Gary Hart when he dropped out and they'll be in the same position in relation to Cuomo when he gets in," Haig contended. Republican voters then will turn to him, he said.