One of the great success stories in American musical life is the San Francisco Symphony Orchestra, which just celebrated its centennial season.

One of the contributing factors to that greatness is the 17-year tenure of music director Michael Tilson Thomas.

You just never know how the chemistry between an orchestra and conductor will turn out over the long haul, whether initial euphoria will give way to ennui (or vice versa).

And whether the inevitable bumps along the way in the relationship -- unpopular decisions about repertoire or personnel, displays of temper, workplace and contract issues, whatever -- will cause a serious or only glancing blow.

But something pretty cool happened right from the start of the union between SFS and MTT, and every indication is that the magic still happens on a regular basis.

There's a lot of recorded evidence of the synergy in San Francisco, thanks to the orchestra's own label, SFS Media, which has produced several Grammy winners. The latest CDs are devoted to works by ...

Collectors can argue whether we really need another recording of Beethoven's Seventh and the "Leonore" Overture No. 3, but I think most folks would gladly make room for the performances that Thomas leads with his ensemble.

What emerges clearly in the first seconds of the Beethoven disc is an orchestra that doesn't just play together, but thinks together, and a conductor who gives the musicians plenty to think about. Dynamics, for example, receive exceptional attention, so that even minute shifts have expressive impact.

Phrases are built organically, meaningfully. The smallest details of orchestration emerge with admirable finesse and color. The strings produce a seamless tone; woodwinds exude character; the brass have bite without turning edgy.

Thomas doesn't offer huge surprises interpretively, but nonetheless assures fresh experiences. There's a palpable tension throughout, even when, as in the coda of the overture, he keeps the tempo in check.

By the same token, although Thomas will not be rushed in the Seventh's relentless finale (I confess a preference for a hell-for-leather, Kleiber-style tempo), he still manages to generate plenty of excitement. Earlier, the conductor brings weight and impact to the second movement, without a hint of a heavy funereal tread.

The absorbing account of the symphony is aided at every turn by the orchestra's remarkably crisp articulation.

The Adams disc contains the snappy "Short Ride in a Fast Machine" and what may be the composer's most profound and stirring work, "Harmonielehre." The latter is a three-movement symphony, a journey of intellectual and emotional complexity, with an air of fantasy woven around the edges. Adams fuses minimalist devices with romantic expression to brilliant effect in this mesmerizing score.

Thomas, who has an innate appreciation for the pulse and prismatic coloring of Adams' music, leads a compelling performance, alert to every shift of instrumental light and shadow, every gradation of tempo. He taps into the soulful passages with great sensitivity, builds to climactic peaks with terrific drive.

The conductor draws stunning, fearless playing from the San Franciscans that may well make you feel like cheering as heartily as the audience.

PHOTO (by BayTaper.com) COURTESY OF MICHAELTILSONTHOMAS.COM