"Mr. President," began the speaker at the podium during the fourth annual Kennedy Center Honors gala at the Opera House, addressing President and Mrs. Reagan in the center box. After a moment's pause, he went on, "and readers of the Atlantic Monthly."

Who else could get away with this, in public, besides Art Buchwald, presidential hair shirt from time immemorial. He was in top form. "Just think, Mr. President," he continued, "if you had not decided to go into politics, you might be sitting in the chair that Cary Grant is in right now" -- another pause -- "and Al Haig would be sitting in yours."

Buchwald was part of the comic relief brigade, no doubt aimed at holding the attention of the millions who'll see the gala later this month as a nationwide TV special. There was hardly cause for worry, however, with a program so packed with celebrities it seemed there was at least one for every paying See GALA, B3, Col. 1 GALA, From B1 customer, including standees. Each of the honorees was eulogized by a personage scarcely less renowned than himself, and a few others were tossed in for good measure. The evening's host, moreover, was the one uncle in America second only to Sam -- Walter Cronkite, in his most avuncular manner.

Mikhail Baryshnikov not only paid verbal tribute to Jerome Robbins, at the show's start, but also danced in an excerpt from Robbins' "Fancy Free" ballet with fellow performers from both American Ballet Theatre (which Baryshnikov directs) and New York City Ballet. Jimmy Stewart praised Helen Hayes as not just the First Lady of the Theater but also "a lot of other things -- she's the First Lady of Kindness, the First Lady of Generosity." Actors Meryl Streep, Donald Sutherland and Richard Chamberlain then delivered a melange of quotes and epigrams on the theatrical life -- Sutherland drew a roar with a line from Sam Goldwyn: "The most important thing in acting is honesty. Once you learn to fake that, you're in!"

Henry Mancini spoke of Count Basie's oustanding contributions to jazz, and Joe Williams and Ella Fitzgerald sang some Basie favorites to the accompaniment of his band; the most impressive music of the evening, though, came from the Basie Band itself, sizzling hot and glorious in sound. Rudolf Serkin's accomplishments were hailed by conductor Seiji Ozawa, and Serkin's youthful prote'ge', pianist Cecile Licad, played a movement from a Saint-Saens concerto with guest Mstislav Rostropovich leading the Kennedy Center Orchestra. For starters, Cary Grant was hailed by Rex Harrison for his "civilized grace and comic brilliance," and as a postscript by Audrey Hepburn for "giving joy across the years."

Amidst all this, the program also found room for soprano Leontyne Price, an honoree herself just last year, to sing a Puccini aria; several extremely amusing routines by Victor Borge (who said he'd decided to honor Rudolf Serkin by not playing the piano); and a barnstorming finish, with performers marching down the aisles and onto the stage, by the cast of the show "Barnum" and members of the Potomac Marching Band.

By now these Kennedy Center Honors affairs are so well formularized that last night's production ran as smoothly as syrup, except for one awkward delay at the end. No amount of preparation, however, can avert the occasional blooper. At Saturday's reception for the honorees, President Reagan called Jerome Robbins Jerome "Roberts," before quickly correcting himself. And on the drop that served as last night's act curtain, bearing the names of all the honorees since the first ceremony in 1978, pianist Arthur Rubinstein's name was consistently misspelled.