Republican presidential candidate George Bush said yesterday that only a thorough overhaul of the energy, economic and international policies of the Carter administration will avert a crisis in the United States in the early 1980s.

In a major speech at the National Press Club, the former ambassador and Central Intelligence Agency director said that any candidate who "promises instant relief" from those problems "is a fraud."

Bush called upon Republican contenders to make "no phony promises" that would lull Americans into complacency about the years ahead.

In the address, reflecting a month of policy conferences with advisers at his summer home on the Maine coast, Bush staked out a number of policy positions that are likely to fuel debate in the coming primary campaign.

He called for the Senate to "correct . . . seriously defective" provisions in the strategic arms limitation treaty with the Soviet Union, and not simply to accept higher defense spending as a rationale for approving the treaty as it stands.

That position put him at odds with former secretary of state Henry A. Kissinger, a colleague in the Ford administration.

On the economic front, he said he favored a Jan. 1 tax cut of $20 billion -- smaller than most congressional Republicans are advocating. The cut should be split about evenly between individuals and corporations, with the main goal of encouraging saving and investment, he said.

In the energy area, Bush urged immediate decontrol of oil prices and called President Carter's proposal for an $88 billion synthetic fuel program "needlessly wasteful." Instead, he said he would "build a limited number of synthetic fuel plants to perfect the technology," and then subsidize expansion of the best designs as much as needed.

The former Texas congressman and onetime Republican national chairman told press club questioners that his relatively low standing in the polls had not inhibited his fund-raising or organizational work.

While conceding that former California governor Ronald Reagan is well out in front in current polls, Bush predicted he would do "well enough in Iowa and New Hampshire" next winter that he would be viewed as a serious challenger to Reagan.

But Bush's main point was that the preoccupation with current poll standings had obscured the "fact that the United States in the 1980s will enter the most dangerous decade in the past 40 years." Economic and energy problems, combined with what he called "the shocking vulnerability of America's strategic forces," could come together in a "thunderclap" crisis in some part of the world, he said.

"The Persian Gulf could become the scene of a second and more deadly Cuban missile crisis," Bush warned.