President Carter, reiterating his support for the Federal Reserve Board's tight money policies, said yesterday that a period of high interest rates is unavoidable in the fight against inflation.

"There is no way we can now avoid high interest rates," Carter said. "The best way to get interest rates down is to get inflation down."

On Thursday, speaking to a labor audience in San Diego, the president appeared to be backing off slightly from his earlier support of the Fed's actions when he declared that "interest rates are too high."

But yesterday, leaving no doubt about his position, Carter said that the Fed's decisions to tighten the money supply and drive up interest rates were a "clear signal" that inflation is the nation's chief economic problem and must be dealt with before all others.

The president made the comments during a two-hour interview program, "Ask President Carter," that was broadcast on National Public Radio. During the program, Carter answered questions by telephone from 28 people from around the country.

The bulk of the questions dealt with domestic issues, particularly inflation and energy. Carter urged energy conservation, passage of his energy legislation and "prudent shopping" by consumers to curb inflation.

But while he predicted a decline in the overall inflation rate by the end of the year, he also warned that energy prices "are going to get higher." He ruled out a tax cut for the moment but left the door open to that possibility later by remarking that "there are some types of income tax reductions that would help reduce inflation."

On foreign policy, the president urged Senate approval of the strategic arms limitation treaty with the Soviet Union, warning that rejection of the treaty would be "a clear signal to people around the world that our country is not committed to controlling nuclear weapons adequately."

Asked about the proposal of Senate Foreign Relations Committee Chairman Frank Church (D-Idaho) to tie approval of the treaty to Soviet assurances that its combat troops no longer are in Cuba, Carter said, "I don't think that's necessary."

The program was the second time that the president had answered questions from radio listeners around the country. The first program, in March 1977, came early in Carter's term, when his popularity was high, in sharp contrast to his low standing in public opinion polls now.

Asked about the polls by program host Susan Stamberg, the president conceded that the national "malaise" he described in a speech last summer in part reflected lack of public confidence in his leadership. Suggesting the approach he will take in seeking reelection, he added:

"I believe that this next year, 1980, a presidential electon year, will serve as a time for presentation to the American people of what I have done as president, the problems that remain and what I can propose in the future to correct those problems. And if I can build up at that time adequate confidence in me when the issues are clearly addressed and that accurate inventory is taken, then perhaps the people will change their opinion."

Carter's reelection campaign indirectly began yesterday with the selection of county delegates to a nonbind-month. While none of the radio program questions dealt directly with presidential politics, yesterday's county caucuses in Florida were on the president's mind when he told one questioner from Jacksonville, Fla., "Don't forget to go to the caucuses today."

On other topics during the program, Carter:

Strongly defended the safety record of the nuclear power industry but pledged to carry out all of the "feasible recommendations" to be made later this month by a commission that is investigating the Three Mile Island nuclear accident. Should the commission find some "inherent defect" in nuclear power, "obviously that would be cause for the terminating" of nuclear power development, he said.

Said he has become convinced that a president should be limited to a single six-year term. Under the historical system of four-year terms with succession, Carter said, there is "too much emphasis by the news media on the political motivations of the president, almost as soon as a president takes office."

Defended his plan to increase defense spending substantially, arguing that the Soviet Union has been outspending the United States in defense for years. "We cannot afford to become weak," he said.