"I am doing this," explained George McGovern, "because my teacher said I had to." The former senator (and former presidential candidate) stood at the Steinway B grand piano in his Connecticut Avenue apartment, responding to polite applause that grew more and more enthusiastic as the evening wore on.

Nobody laughed, exactly, when McGovern sat down at the piano, but the attitude--particularly from his political peers and colleagues, Sen. Edward M. Kennedy (D-Mass.) and former senators Frank Church and Dick Clark, was one of healthy skepticism. By the end of the evening, McGovern, who has been studying the piano seriously for only about six months, won ungrudging admiration, if not entirely for his musical technique, at least for his grace under pressure.

Before the concert, McGovern mingled with guests who were sipping cocktails, urging them to brace themselves for the experience. "You don't look nervous," said Kennedy, shaking the hand that was about to launch into "Maple Leaf Rag" and "Embraceable You." "Usually, before they go on, virtuosos are locked away in a room somewhere, practicing and exercising their fingers." Church volunteered limited assistance: "I can play the Mickey Mouse March," he said. "I learned it when I was 6."

Explaining why he was performing before an audience, McGovern gestured toward his teacher, pianist and composer Harvey Jacobson of Gaithersburg. "One of the conditions under which Harvey agrees to take a pupil," he said, "is that you agree to do a public recital. I didn't understand that until about a month ago . . . but it really focuses your attention."

Then he sat down and began playing Scott Joplin's "The Entertainer"--a shade slowly, but Joplin posts warnings against playing too fast all through his sheet music. Throughout a program that included Richard Rodgers, George Gershwin, Harold Arlen and Kurt Weill, the interpretation reflected the pianist's character, as a good performance always does. It was not flashy or spectacular but thorough, thoughtful and earnest.

The playing was impressive for a student who has been studying for only six months. All of the tunes were immediately recognizable, and McGovern got almost all of the notes right the first time. Once, going into the second chorus of "Oh, What a Beautiful Morning," he made a false start and began again, but he carried on like a pro. At the end of the number, he looked at his watch and got laughter from the audience. "All right," he said, "we're getting there," and launched into "Mack the Knife."

Since his not an entirely voluntary withdrawal from politics, McGovern has been doing what political exiles often do: a bit of writing, public speaking, teaching at a university. But he added a purely amateur interest in music to his pastimes and was surprised to discover that he had to do it with people listening. At first, the guest list for his debut recital at home was limited to a few friends, family members, colleagues, his teacher and Donna Byson, manager of Jordan Kitt's downtown store, who was proudly telling people, "I sold him the piano."

But word got around and the audience grew. By the time he began to play, there was a camera crew from NBC and the prospect that he might be seen on this morning's "Today" show. A sound technician held a microphone under the piano on a long handle, and the informal audience assumed the posed air of people who know that they may be on camera.

Earlier, Mary Hoyt, who was Rosalynn Carter's press secretary, was asking teacher Jacobson about her new piano (she, too, is a political exile). "I studied piano years ago, since I was 6," she said, "and now I'm returning to it with a vengeance--but I can't understand what the middle pedal is for." Actually, Jacobson explained, "it isn't for much of anything. It used to have a use 100 years ago, but now it just makes the piano look right."

Besides his solos, McGovern played accompaniment for a singer, Mary Blankemeier, who has a good country voice with a nice, smoky tone. And as an encore, teacher Jacobson and tenor Douglas Jimerson performed two songs from his next album, a song cycle called "Coins of Gold."

"I thought he played very well," said Kennedy after the performance. "My only criticism is that there were no Irish songs." This was enough to launch Jacobson and Jimerson into the impromptu rendering of "When Irish Eyes Are Smiling" and "My Wild Irish Rose."

"There's a strong demand that you be joined by Teddy Kennedy," said McGovern, interrupting the musicians. "When George can play it, I'll sing it," said Kennedy. And that was the end of that.