Sooner or later, all presidents come to view news conferences as exercises in damage control. Yesterday, Ronald Reagan booked a basically safe passage through the East Room aboard a time-tested vehicle, using generalities and vagueness in place of pointed, detailed responses.

More than ever, Reagan found himself on the defensive as questions that came his way were more barbed than those in the four other news conferences of his 10 months as president. More than ever, reporters pressed follow-up queries when Reagan sought to steer clear of the controversies placed before him.

"We did all right," said one top-level adviser when the conference had ended. "That was a pretty tough job he had out there today."

All but a couple of the questions were based on premises clearly critical of administration policies and conduct. The pattern was established at the outset.

The opening question, on international affairs, asked about the "high state of belligerency that seems to personify" Reagan's foreign policy. The next one, on domestic policy, asked what assurances Reagan could give Americans about his budget promises, now that he has conceded that his original pledge of a balanced budget by 1984 cannot be met.

At times, Reagan sought to steer clear of the subject at hand, as when he was first asked about his seemingly reasonable statement--which touched off a furor in Europe--about how a single tactical nuclear weapon could be fired in a European battlefield without global nuclear holocaust resulting.

"I won't repeat it here," the president said, gingerly picking his way through an explanation of what he had said.

But a couple of questions later, Bill Plante of CBS television, followed up, and this led to Reagan's most difficult moment of the day.

Plante read the original offending passage from a transcript and pressed for a further explanation, in light of the subsequent dispute between Secretary of State Alexander M. Haig Jr. and Secretary of Defense Caspar W. Weinberger. Haig had testified that NATO had a contingency plan allowing a nuclear warning shot in the event of war with the Soviets, and Weinberger testified the next day that he knew of no such plan.

Reagan, seeking to settle things once and for all, wound up making the same assertion, one more time, that had so rattled the Europeans. Then, pressed about the Haig-Weinberger conflicts over the idea of a nuclear warning shot, the president said:

"Oh, well, that--there seems to be some confusion as to whether that is still a part of NATO strategy or not, and so far I've had no answer to that."

This pressed presidential aides into participation in another tradition of the American presidency: the post-news conference clarification. "He knows the answer," said one of the president's most senior advisers. "I don't know if he just forgot it for a moment or not."

The president was asked by chief of staff James A. Baker III how the matter should be clarified and, within minutes, deputy press secretary Larry Speakes was working the press room, and communications director David Gergen was working the phones, dutifully spreading the official word.

"The president was concerned whether it was something he could properly discuss," Gergen said, in clarification. Speakes offered puckish elaboration: "He knows the answer. He just doesn't want to tell you."

Reagan survived his half hour of trial by fire in part by lengthening his responses and successfully limiting the number of questions. He was asked just 17 questions and follow-ups; in his past news conferences, the number of questions was always in the mid-20s.

Reagan came armed with a joke. Asked about well-publicized disputes among his foreign policy advisers, he said: " . . . the only thing that seems to be going wrong is, I think sometimes that the District of Columbia is one gigantic ear."

He also had the electronic aid of a little black box. White House communications experts had installed a loudspeaker at the left of the president's podium, just below camera range. It amplified the questions for Reagan, who suffers from a loss of hearing and had misunderstood a question in the previous news conference, leading to an erroneous answer.

Yesterday, the questions may not have been to the president's liking, but they came in loud and clear, thanks in part to the electronic ear.

EPILOGUE: From his retirement in West Virginia, Bryce Harlow, who advised three Republican presidents and was awarded the Medal of Freedom by the current one, was reflecting upon another venerable institution of the American presidency: the news conference.

"There are times when the press seems favorably disposed toward a president," he said, "and then the press conference becomes an opportunity, a chance to make a sale. But there are times when the press is, shall we say, less favorably disposed. And then the press conference becomes an exercise in damage control.

"It all depends on the ambiance of the press."