Recently, President Reagan called reporters into the Oval Office for a televised press conference. That was the one in which he said he was optimistic about arms reductions, that South Africa was morally wrong but tactically right, that he was not giving up on tax reform and, yes, now that you ask, that pimple on his nose had been cancerous. Then turning to his pals, the press, the president asked why they did not meet with him more often. But he already knew the answer. He refuses to.

It would be harsh to categorize what the president said as a lie. It is really something else -- a genus of untruth that has its roots in show business and therefore is considered to be of little consequence. It is, in short, a performance -- the sort of thing you see on the Johnny Carson show. Carson asks a guest why he's not on the show more often and the guest says something about being busy -- Vegas and all. The truth is that he'd kill to be on the show more often.

In Reagan's case, the truth is that the press would love to have more news conferences. It lobbies for them, and from time to time a reporter writes an article about how Reagan has held fewer press conferences than any president since Martin Van Buren. So why did Reagan say what he did? The answer, I fear, is that he sees the press conference as just another aspect of show business. His banter to the press was in the nature of a guest's chat-'em- up with Johnny Carson.

Don't get the idea that this phenomenon is limited to Reagan. The president may be the most accomplished actor in town, but he is far from the only one. Many of the town's politicians long ago learned that, while the camera may not lie, you sure as hell can lie to it. Recently, a member of Congress appeared on a television show to debate the merits of a movie. He praised it. He said he loved it. He ripped into anyone who was critical. It was only after the show was over that he admitted he didn't particularly like the movie. You guessed it: just another performance, folks.

The press, too, seems infatuated with the importance of performance. Washington has talk shows in which journalists compete to see who can combine the politics of Francisco Franco with the demeanor of Dennis the Menace. Most of the participants are fine people, and some of them have gotten rich and famous for their ability to deliver a quip under pressure. This has not been lost on others who are not yet rich or famous and who know that television can make you both. That's why there are some in the Fourth Estate who will say almost anything while on television -- things they do not for a moment believe and would never put down on paper. Television, though, is different. It's the performance that counts.

But old-fashioned honesty ought to count for something. The premise of all these show biz lies is, after all, that the public merely wants to be entertained. Maybe that is the case when it comes to the Carson show or a verbal food fight among journalists. But presidential news conferences ought to have a different hierarchy of values. Instead, the value seems to be that nothing is as important as the performance.

Ever since John Kennedy, the televised press conference has been used not just to inform the public, but also -- and increasingly -- to enhance the presidential image. With Reagan, the attempt is always to show him at what he is not -- informed and up on the details of government and, thus, willing at any moment to have a press conference. Reagan may be many things, but well- informed is not one of them.

Probably for reasons having to do with respect for the presidency and not wanting to appear rude, the press played Ed McMahon to Reagan's Johnny Carson. When he asked, "Where have you all been keeping yourselves?" the best someone could do by way of an answer was to say, "You should do this more often." Ah, but he does.

He does it all the time.