President Reagan didn't slip up or break new ground Thursday at what was supposed to be his 28th news conference. He didn't because his keepers at the White House decided that the time wasn't right for answering questions and canceled the news conference before it was announced.

Eighteen years ago at this time, heading into his second term, President Dwight D. Eisenhower had completed his 99th news conference. Reagan's predecessor, President Jimmy Carter, held 59 in the four years he was in the White House. Even President Richard M. Nixon, who detested the Washington media and found news conferences an ordeal, had held 30 news conferences by the end of 1972.

There is no magic in these numbers. Reagan has communicated in other ways with the American people. He has made 26 nationally televised speeches during his presidency, given 194 interviews, held "mini news conferences" like the one Friday and occasionally has taken serious questions at the "photo opportunities" so beloved by his White House advisers.

By and large, however, Reagan has shunned news conferences like a mortal plague. In the last half of this year he has held two, one on July 24 and the other on Nov. 7, a see-you-at-the-ranch session as he headed out the door of his Los Angeles hotel the day after his reelection.

White House deputy chief of staff Michael K. Deaver, the president's chief media adviser, at least has the virtue of candor in explaining why Thursday's news conference was canceled and why no others are scheduled in 1984.

"We had not made the decisions on the budget or the tax plan," Deaver said. "We really didn't feel a great sense of pressure to hold a news conference. The time to put him out there would be after the holidays when people begin focusing on policy."

This comment contains an implied -- and deserved -- rebuke for those of us in the White House press corps, who have not been as insistent as we should be in calling for news conferences. The White House press office also appears to have struck out. Larry Speakes, the principal deputy press secretary, has proposed that Reagan hold weekly sessions with the media, but the only response has been the Friday appearance that Deaver approved at the last moment.

But the view that Reagan should be hidden until troublesome issues are resolved is even less flattering to the president than to the media. It could be seen as unintended ratification of the charge that Reagan is too ignorant or uninformed to be allowed in public without a prepared speech. It also could be read as the kind of second-term arrogance that comes before a fall.

In fact, Reagan isn't arrogant, and he does better at news conferences than either advisers or critics recognize. What he lacks in precision, which is considerable, he more than makes up in conviction and strength of purpose.

During Reagan's first term as governor of California, when he was vastly less informed, he held weekly news conferences. He did all right. As a performer who thrives on practice, he tended to become sharper when he regularly faced the media. Reagan's advisers also found it easier to brief him when they had only a week's events to worry about.

These days the advisers, encouraged by Nancy Reagan, behave as if a news conference were a long-postponed visit to the doctor where the patient is afraid of what he might be told. Their tactic is to wait until the clamor from the media becomes intolerable and then shove Reagan out into the East Room as if he were a Christian in early Rome being thrown to the lions.

Other presidents, such as Franklin D. Roosevelt and Eisenhower, recognized that news conferences serve a national purpose even after landslide victories. In terms of responsible governance, a claim to which Reagan ought to be responsive, news conferences serve the purpose of making the president accountable and accessible.

Beyond the civics-books arguments and the obvious interest of the media in more frequent news conferences, Reagan's advisers ought to show a little more respect for the president they claim to serve. With the economy declining and the stock market skidding, it is in the interest of the country for Reagan to come out of hiding. A case could be made that it also is in the interest of the president.

Reaganism of the Week: When Reagan was posing for pictures Tuesday with White House social aides, one asked him what he would like for Christmas. "Well, Minnesota would have been nice," he said, referring to his reelection win, in which he lost only Minnesota and the District of Columbia.