Nancy Reagan, snowed out of attending Soviet e'migre' Vladimir Feltsman's American debut at Carnegie Hall Nov. 11, managed to catch his sparkling Kennedy Center debut last night in fine style. And on this occasion -- unlike what would have been the case for the aborted trip to New York -- she was even able to bring her husband along.

It was an evening of wild enthusiasm, expressed in standing ovations -- two for the Reagans and two for the pianist, who had to work somewhat harder than the First Fans to earn his.

The Reagans got their first just for walking into the presidential box with the pianist's wife Anna, and they didn't even have to get there on time. They arrived at 8:10 for a concert scheduled to start at 8. But that didn't matter; a lot of people arrived late, after fighting their way through crowds of onlookers that blocked the entrance to the Grand Foyer and then waiting in line to pass through one of the three metal detectors that were set up behind the ticket-takers.

Feltsman, a refusenik for eight years before being granted an exit visa this summer, waited until the president had waved to the audience and settled comfortably into his seat, then bounded onstage in his usual energetic style, bowed and launched into a precise, nicely understated interpretation of Schubert's sweetly melodious Sonata in A, D. 664.

The Reagans got an even more enthusiastic ovation when they returned to their seats after intermission, and this time Mrs. Reagan joined her husband in the waving. He did it with professional panache, she with a touch of diffidence.

At the end of the concert, while the final, smashing chords of Schumann's "Etudes symphoniques" were still reverberating, the Reagans were the first on their feet to express approval of the performance, but the whole audience followed their example seconds later. Feltsman also received a standing ovation after his second encore, and probably could have milked the situation for more if he had chosen. But he had a quick appointment backstage with his favorite fans.

Concert patrons were politely but firmly directed away from the backstage area while the First Couple came to visit, but the disruption did not last long; by 10:15, the presidential motorcade was whizzing through the blocked-off streets for the short trip back to the White House.

Feltsman showed again what he had shown last month in a private performance at the White House -- that he is a pianist of immaculate technique and solid musical instincts, with a fine knack for building interesting programs with little surprises. The unusual part of this program was its central selection, three of Messiaen's "Vingt Regards sur l'Enfant Je'sus" -- ecstatically mystical music that only the most brilliant technicians can aspire to perform, only the most intrepid modernists would dare to put on a program, and only the most inspired keyboard poets -- the kind who usually play a lot of Chopin -- can interpret effectively.

Feltsman did the music full justice, and without asking how a Jewish musician raised in an atheistic society managed to become so sympathetic to this intensely Christian music, we may simply rejoice in the result.

A whole Schubert sonata was perhaps a shade ambitious as a program opener; one wants something fairly light while the pianist's fingers are settling down for their evening's work. But the Sonata in A, composed for a pretty young lady named Koller, with whose family Schubert dined regularly in the summer of 1819, is as light and melodious as a series of nursery rhymes, with only enough shadows for a bit of contrast and a little bit of gee-whiz thrown into the last movement.

The Schumann etudes are as searching a test of a pianist's abilities as any music in the repertoire, and a thoroughly enjoyable series of variations as well. Feltsman's interpretation brought out all their kaleidoscopic variety and he rose with no apparent effort to their multiple and varied challenges.

It is too early to make a final assessment of what we have gained in the person of this smart, skilled and highly likable young musician who finally was allowed to emigrate from the Soviet Union. Feltsman is certainly a brilliant, thoughtful, imaginative pianist whose work is well worth attention. Whether he is one of the transcendent musicians of our time remains to be seen, and probably does not really matter.

He comes to an America that is certainly not suffering a shortage of outstanding pianists, but he comes clearly with a level of talent that will assure him a solid place in our musical firmament for the next generation. It is entirely possible, on the evidence of his first recitals here, that he may develop into one of the giants, on the level of a Serkin or a Brendel; at 35, he is still young to be active on that level and enormously talented. It should be an interesting and joyful experience to watch his growth