The blossoming of a brilliant conductor

Michael Tilson Thomas shot to stardom overnight when he replaced an ailing William Steinberg midway through a New York concert by the Boston Symphony Orchestra in 1970.

There was the expected flurry of attention, the all-too-usual predictions that a fully formed musical star was now upon us. There was the optimistic assumption by many that Thomas and the BSO were partners for life. But he was very young, the orchestra rather crusty. After several years, an undercurrent of acrimony was evident on the part of the orchestra whenever Thomas took the podium.

So Mr. Thomas began roaming the guest-conductor circuit and also became head of the Buffalo Philharmonic. He was able to grow, to mature, to try things out, even to make awful mistakes - all the things a fledgling artist must be allowed to do (and conductors usually remain fledglings until they are approaching 50 years of age). And he could do it all out of the cruel spotlight of a major podium.

There was always the spark of the unusual in Thomas. I remember a try at Mahler's Ninth Symphony in Boston that was surprisingly good, considering no youngster could ever hope to have the emotional and interpretive depth to come to terms with this tortured, agonized work. Also in Boston, his reading of Stravinsky's ''Petrouchka'' ranks as the finest I have ever heard in a concert hall - lithe, taut, yet lyrically persuasive and downright beautiful when called for. He recorded the same composer's ''Le Sacre du Printemps'' to great effect with the BSO, as well as Debussy, Ives, and Ruggles.

I also vividly recall his aching, haunting reading of the complete three-act version of Alban Berg's opera ''Lulu'' in Santa Fe in '79. This memorable performance also served to remind the listener that Thomas was maturing very impressively. A few seasons back, he conducted Janacek's touching ''The Cunning Little Vixen'' at the New York City Opera and scored another triumph, proving his gift in unusual repertoire and his facility in an opera house.

He is now a principal guest conductor of the Los Angeles Philharmonic, is recording a Beethoven symphony cycle with the English Chamber Orchestra, and has also recorded a nice quantity of unusual works by famous composers for CBS. Most recently, Thomas was the last-minute replacement for a convalescing Zubin Mehta (who is out for the rest of the New York Philharmonic's season due to an elbow disorder). Once again, the conductor showed off new strengths.

The concerto on his program was Beethoven's Fourth, with Alexis Weissenberg. Thomas proved to be an attentive accompanist for the pianist's remote, rarefied, unappealing account of the piece. But it was in that war horse, Tchaikovsky's Fifth Symphony, that Mr. Thomas really had a chance to shine. He reduced the number of strings to allow the balances in the winds to be more prominent and audible. He chose to avoid bluster and bombast in a piece most conductors try to show as a vision of Armaggedon. For Thomas, this piece clearly thrives on a propulsive lyricism, and he suffused the entire performance with an electric yet elastic tension. This refreshingly rethought approach to Tchaikovsky illumined rather than rehashed, and it represented the very best of a Michael Tilson Thomas who is steadily fulfilling his extraordinary potential.

His recent program opened with Leonard Bernstein's ''Divertimento for Orchestra'' - an entertaining ''curtain-raiser'' commissioned by the BSO for its centennial celebrations in '80. Thomas gave it sparkle and elan, and he had fun with the piece as, apparently, did the players. Bernstein was then presented with a scroll, making him an honorary member of the New York Philharmonic - an honor also conferred on Mahler, Mendelssohn, Copland, and precious few other musical luminaries.

Bernstein and a revitalized Philharmonic

Leonard Bernstein recently conducted a ''Program for Spring'' as a replacement for Rafael Kubelik, who was forced to cancel his Philharmonic dates this spring. The program had opened with a beautiful, thoughtful performance of Copland's ''Appalachian Spring,'' continued with a brooding, energetic, and suitably impulsive journey through Schumann's First Symphony, subtitled ''Spring.'' However, the piece de resistance of this generous program proved to be a thoroughly barbaric, hedonistic, and resplendent rendering of Stravinksy's ''Le Sacre du Printemps.'' Yet with all the primitivism unfurled in the performance, Bernstein managed to make it surpassingly beautiful - and eerie and subtly mysterious as well. Earth-shattering decibels were not employed as the excuse for every climax, but rather each eruption was carefully prepared, thoughtfully built, and stunningly well balanced.

As is increasingly the case these days, the Philharmonic performed both programs very well indeed. There has been such an about-face with this orchestra - a more concentrated care on putting its best image and best sound forward. They have a way to go in enriching string tone and smoothing out the brass. But then again, unless the acoustics in Avery Fisher Hall are smoothed out as well, no orchestra would be able to fine-tune its tonal amenities. Interestingly enough, Mr. Mehta had begun experimenting with a radical reseating of the orchestra to attempt to make the best of a problematic situation. Next fall promises to be an interesting time in this regard.