For longer than some of its players have been alive, Seiji Ozawa has been conducting the Boston Symphony Orchestra. When he leaves Boston in 2002, he will have led the orchestra longer than Serge Koussevitzky, who helped put it on the map as one of the Big Five. On Saturday afternoon the 64-year-old Ozawa brought his orchestra to the Kennedy Center, and it has never sounded better.

When Ozawa took over the chief position in 1974, the BSO was considered one of the finest orchestras for French music in this country. Ozawa's intention was to build on that sound, to add more gravitas to an orchestra renowned for the clarity and agility of its playing. There were detractors along the way who blamed the brash but aloof young maestro for sullying a proud tradition with this darker sound.

But now it's clear that Ozawa, at the height of his powers as a conductor, has been a diligent steward of the orchestra. On Saturday it played both Brahms and Debussy, and both sounded just right. Ozawa's Debussy (he conducted "Nuages" and "Fetes" from the "Nocturnes") had the precision of Pierre Boulez's hyper-attentive modernist approach, and a shimmer of pure sound that might have come from Pierre Monteux or Charles Munch. His Brahms Symphony No. 3 had the requisite weight of sound, the lushness of string texture, but it, too, had a shimmer, and its structure--the joints and joists of its overall layout--was transparently clear.

Long marriages such as Ozawa's inevitably attract critics. Ozawa has never been accused of being a people person, and his musical style is based on absolute confidence and knowledge of the score--which can threaten other musicians.

While other conductors have embraced the jet-age lifestyle that precludes more than a few months of the year spent with any one group, Ozawa has resolutely focused on Boston. If the marriage soured, it never became apparent from the group's playing. The connection between conductor and musicians is intense and instantaneous. In Lutoslawski's Concerto for Orchestra--which, played well, is one of the greatest works of this century, and, played poorly, one of the longest sits in the entire repertoire--the immediacy of the players' response made a difficult score sound fully lived in and expertly assimilated by every section of the orchestra. Ozawa conducted this, and indeed the entire program, from memory. That kind of deep penetration is rare, and only when one hears its effect on a thorny and complicated work does its virtual absence in the modern concert hall seem so glaring an oversight.

When Ozawa first arrived in Boston in the late 1960s, he seemed to represent a break with tradition. He rode motorcycles and conducted in turtlenecks. Now, with gray in the famous mane, he seems to be the quintessence of a fading professionalism in the star conducting business. The orchestra was, of course, on display Saturday. Perhaps they don't always play that well. But if they hit that mark at least 50 percent of the time, Bostonians are very lucky indeed.

In the two Debussy movements, the tone of the group was as clear and resolutely reliable at the extreme ends of the music spectrum as it was in the middle range. The musicians played very softly but with fully realized depth to each note; nothing grew hazy or fuzzy at the edges. In the Brahms, they found an ideal balance of Mozartian classicism and Brahmsian weightiness. It was Brahms with the windows open, structurally solid but never pedantic. The final pages of the last movement, a quiet but sunny walk into the distance, were hauntingly effective.

The BSO came to Washington without a star soloist on the program. In the Lutoslawski, the players themselves were on display. One didn't miss hearing an underrehearsed pianist or violinist in the least.

CAPTION: With a quarter-century under his baton leading the Boston Symphony, Ozawa is at the height of his powers.