Politics has been a branch of show business since democracy was invented, but it was not until 1981 that a card-carrying member (and former president) of the Screen Actors Guild was sworn in as president of the United States.

How have Ronald and Nancy Reagan done in their first four years as the proprietors of what has become a prime showcase for the performing arts in America? The review must be mixed -- seldom very good or very bad but, on the whole, as good as could be expected. The White House's choices of entertainment for state dinners and other gala occasions have been predictably conservative. There have been relatively few surprises, occasional small embarrassments, but no real fiascoes.

It is not fair to blame Ronald Reagan for the Great Beach Boys Flap of 1983, which related to a performance on the Mall, not at the White House, but led to a Beach Boys gig at 1600 Pennsylvania Ave.

Nor is he really responsible (except as a commander in chief is always responsible) for the time when Secretary of State George Shultz was accidentally greeted with "Send in the Clowns" as he came in through the Diplomatic Entrance for a state dinner. Or the episode of confusion over the Austrian national anthem. Or the time when Rich Little (a guest) did his Richard Nixon imitation for Richard Nixon (also a guest). Or the evening when Robert Goulet told off-color jokes to a White House audience that included the late Terence Cardinal Cooke, archbishop of New York. Or the mistake of inviting Mort Sahl to an evening of classical music that later found its way into one of his comic routines.

"At last, we will have a return to elegance at the White House," a guest was overheard sighing at a presidential social function early in the Reagan administration. She may have been thinking of the outdoor barbecues, the gumbo and jambalaya that were served on the South Lawn of the White House during social functions in the Carter administration -- a reception for stock car race drivers, with Willie Nelson topping the list of entertainers, or a marathon jazz festival with Lionel Hampton (who was supposed to be performing) and Pearl Bailey (who was not) struggling for control of the stage. Perhaps she recalled one of the most vivid moments in White House social history, when Dizzy Gillespie badgered Carter into singing the two-word chorus of "Salt Peanuts" into the live microphones of National Public Radio.

"Ain't no bigger show than playing for the president," Lionel Hampton told an audience on the South Lawn in 1981. He should know; he has played for six -- a fair score for a musician who has been a headliner in the administrations of nine presidents. A lifelong Republican, Hampton unconsciously echoed the lady nostalgic for elegance when he reminisced about a previous White House performance, at Carter's jazz festival: "At that one, they had a barbecue. At this one we have caviar."

Sometimes the Carters entertained elegantly, though their liquor stock was neither choice nor lavish. There was a reception for poets, with simultaneous readings going on in several rooms of the White House, and there were frequent moments of musical enchantment from performers who ranged from Vladimir Horowitz to Shirley Verrett. And when it was not elegant, it was vivid. Whether or not you enjoyed his singing voice, Carter looked like a hard act to follow in the role of First Impresario.

But Reagan has done a decent job of it. His personal tastes may or may not be reflected in the entertainment (mostly music; occasionally dance or a movie such as "E.T.") in the East Room or on the South Lawn. Sometimes, when the music is pop or jazz, the guiding taste seems to be that of Frank Sinatra. And if the Carter White House sometimes sounded like Georgia North, the Reagan White House sometimes sounds like Las Vegas (or Lake Tahoe) East.

Still, the Reagan staff, particularly Nancy Reagan's, has clear (and usually accurate) ideas of the entertainment appropriate for a given occasion -- material that will mildly please most people in a chosen audience and seriously displease hardly anyone. Hard rock music has been scrupulously avoided -- the Fifth Dimension and the Beach Boys are about as close to that as the Reagan White House has come. But otherwise, there has been a fair sample of American musical life, ranging from Zubin Mehta and the New York Philharmonic to Red Steagall and the Coleman County Cowboys, a country and western group from Fort Worth. This has been done on a minimal budget. Performers are never paid for appearances at the White House and only in exceptional cases are they given expense money. The Philharmonic's trip to Washington, for example, was subsidized by Citibank.

The Coleman County Cowboys and the New York Philharmonic, like many other entertainers in the past four years, were essentially ethnic choices. Mehta was chosen to play for the late Indira Gandhi, prime minister of his native India. Steagall and company played at a reception on the South Lawn for the Professional Rodeo Cowboy Association, whose act Reagan caught at the Capital Centre, crossing a picket line set up by humane societies. Sinatra's influence has been felt often in his friends' performances at the Reagan White House. But he has sung at only one of Reagan's state dinners, when it was ethnically indicated. That was for Italian President Sandro Pertini, and the other singer on the program was Perry Como.

The ethnic touch backfired seriously last year at the state dinner for President Rudolf Kirchschlaeger of Austria, an affair that seemed ill-omened from the start, when Tommy Tune and Twiggy, originally scheduled to entertain, backed out after they had done a command performance for Queen Elizabeth II and discovered how much it could disrupt their working lives. Mel Torme' and Peter Nero filled in and inspired one of the few less than enthusiastic comments ever uttered publicly by a guest at a White House musicale. Asked how she enjoyed the music, the formidable Baroness Maria von Trapp replied with a question: "May I not say what I thought of it?"

Neither did the Austrian delegation know what to think of the Rodgers and Hammerstein song "Edelweiss" from "The Sound of Music," inspired by von Trapp. Reagan quoted the song in his toast to Kirchschlaeger, and the Austrians heard it played wherever they went. "There are 200 million Americans who know it's the Austrian national anthem," U.S. Trade Representative William E. Brock III told Austrian Ambassador Thomas Klestil. Klestil recalled an occasion in Texas when he was invited to sing along: "I didn't know the words. I said, 'It is not an Austrian song, it is a movie song written in Hollywood.' When I said I didn't know the words, they were shocked and they looked at me as if I were not a patriot." "You mean it isn't the Austrian national anthem?" asked Laura Brock.

Americans cannot be expected to know such things, and American presidents are not held to unrealistic standards in musicology. "I only know two tunes," said Ulysses S. Grant. "One of them is 'Yankee Doodle' and the other one isn't." This deficiency did not keep him from serving two full terms, and Carter's love for all kinds of music did not win him a second.

There are clues to the level of musical interest in the Reagan White House. One was given in the summer of 1981, when the first American performance of Mozart's recently discovered Symphony in F, K. 19A, was given on the South Lawn. Reagan delivered his script with the right expression, but nobody had told him that the name of Mozart's friend Haydn should be pronounced to rhyme with "widen," not with "maiden."

Still, the staff has seen to it that the classical music performed in his White House is, if not abundant, at least certifiably first-class. At a 1981 reception for Menachem Begin, for example, the performer was Andre'-Michel Schub, winner of the Van Cliburn Competition. Unfortunately, Mort Sahl was also there. In a nightclub routine the next year, he described the event with Secretary of State Alexander Haig and Defense Secretary Caspar Weinberger falling asleep and "their wives . . . giving them the elbows-in-the-ribs routine." Other classical performers heard at the White House in the last four years have included Rudolf Serkin, Isaac Stern, Pinchas and Eugenia Zukerman with pianist Marc Neikrug, Sherrill Milnes, Robert Merrill and Anna Moffo, the Chamber Music Society of Lincoln Center, Beverly Sills and Leontyne Price -- gilt-edged names one and all; risk-free programming.

Less-known but eminently worthy performers have also been heard, but usually in special contexts -- the Folger Consort, for example, in a program celebrating the Folger Shakespeare Library's 50th anniversary, which gave Reagan a chance to quote a bit of Shakespeare. Some White House performers -- Serkin, Sills and Price, among them -- have brought along younger, less known artists to share the spotlight in the "In Performance at the White House" series that has been telecast on PBS in recent years. The program (which has been quiescent recently) was always hosted by well-known classical musicians -- Sills in 1981, Itzhak Perlman in '82 and Price in '83 -- but the performers have been largely popular artists with a mass following: Gene Kelly, Merle Haggard, Dizzy Gillespie, Mary Martin and John Raitt, for example. Along with Serkin, Perlman and other world-famous classical musicians, the series has spotlighted some younger (though hardly unknown) performers such as pianist Ken Noda and soprano Ashley Putnam.

Reagan's musical orientation is clearly stronger than that of U.S. Grant; how much stronger is an unanswered question. He seems to respond most happily and spontaneously to pop entertainers, particularly country music and the jazz styles of his youth. "Aren't we glad we grew up in the era of the big bands?" he once asked an audience of 900 on the South Lawn. The strong, simple messages of country music seem to have a kinship with his own view of the world. After Tammy Wynette sang "Stand by Your Man" for him, he told her: "I'm going to get a record of that and send it up to the Hill."

Pop performers in the Reagan White House have ranged from Juice Newton, Wayne Newton and the cast of "Sophisticated Ladies" to Benny Goodman, Buddy Rich and Ella Fitzgerald. Occasionally there is a daring choice like Julio Iglesias (at a state dinner for Franc,ois Mitterrand, who evidently required something out of the ordinary). It is safe to estimate that, if White House performers were elected by Reagan's constituency, the list -- classical and popular -- would be essentially the same.

If the choices can be criticized, it is chiefly for a policy that seems to parallel Reagan's orientation in other areas. With few exceptions, the benefit of the White House spotlight is withheld from the needy and bestowed most lavishly on those who need it least. But nowhere has the president been given a mandate to discover and promote fresh talent when there are plenty of celebrities around, willing to add glitter to the presidential mansion.

Frequently, there is even more glitter (sometimes glitter from the remote past) in the guest list than in the program. Occasionally, that list includes classical musicians. Cellist Yo-Yo Ma, for example -- invited (following the ethnic principle) to a reception for Chinese Premier Zhao Ziyang. Or pianist Byron Janis, who may have been there because he is Gary Cooper's son-in-law.

Any White House guest list is likely to put heavy emphasis on key politicians and high executives in industry and the media; Reagan's certainly did in his first four years. There are also the people appropriate (ethnically or professionally) for a particular occasion. But the distinctive flavor of an administration's social life comes from the kind of people who don't strictly have to be invited but are: the president's friends and the people with whom he wants to enjoy himself.

The guest list at Carter's musicales was often a Who's Who of American musicians. Reagan's frequently reads like a Hollywood Who Was Who: Jimmy Stewart, Ginger Rogers, Helen Hayes, Kirk Douglas, Eva and Zsa Zsa Gabor, Cary Grant, Dinah Shore, Olivia de Havilland, Phyllis Diller -- not to mention such representatives of youth as Rock Hudson and Pat Boone.

If the trend continues and Reagan manages to change the country's fiscal policies, an occasional free meal for an aging thespian may turn out to be his administration's most significant form of support for the arts. In recent years, at the classier performing arts events in the White House, Reagan has enjoyed ringing variations on a familiar theme that usually goes something like this: "Here in America, we support more theaters, opera companies and concerts through private contributions than all the rest of the world, with its government subsidies, put together." Accurate or not, it was an effective statement until proposals began to surface for legislative changes that would wipe out most tax incentives for private contributions to the arts.

The Reagan family's most prominent involvement in performing arts to date (not counting his son, the former dancer) was considerably more complex and demanding than Jimmy Carter's chorus of "Salt Peanuts." Not long after the death of her friend Princess Grace, Nancy Reagan substituted for her as the narrator in a National Symphony pension fund concert, reciting the verses written by Ogden Nash to go with Saint-Saens' "Carnival of the Animals." It was impressive, and it did result in a substantial benefit for the arts in Washington. In memory of the occasion, Sultan Qaboos Said of Oman (who needs no tax incentives from the IRS) presented a $300,000 endowment to the National Symphony for a Nancy Reagan chair of narrative music.

From now on, whenever a narrator performs "A Lincoln Portrait," "Peter and the Wolf," "The Martyrdom of Saint Sebastian" or other works for narrator and orchestra with the NSO, the event will be a tribute to Nancy Reagan. That may be the most permanent memento of the current first family's impact in the performing arts -- that and, of course, reruns of her husband's movies on the late-late show.