Richard Strauss' "Ein Heldenleben," that enormous, heroic, sumptuous and -- above all -- deeply human tone poem, was given a magnificent performance last night at the Kennedy Center by the National Symphony Orchestra under Michael Tilson Thomas.

As Tilson Thomas himself remarked recently about somebody else's performance of another work, it was one of those "on-the-edge-of-your-seat things."

But this "Heldenleben" was also something considerably more than that.

As to the conductor's interpretation, there was remarkable steadiness from the work's urgent opening -- with Tilson Thomas' breakneck tempo at the first -- through its 45-minute span to the sad, resigned -- and very slow -- end.

It was a very passionate view of "Heldenleben," a work that will fall into tedious episodes if done tepidly. Tempos, textures, and phrasings were very skillfully calculated. And the work's underlying pulse remained steady, even in such a section as the hero's lovemaking, played with broad rubato and eroticism. "Heldenleben's" moment of greatest majesty, when the opening theme returns after the battle music, was beautifully prepared for, and played with imposing breadth.

Then there was the orchestra. Tilson Thomas has a way of getting an orchestra wound up when he himself is excited. And the excitement sizzled last night.

Playing became more opulent as it went along (ensemble at the very start was a little blurred).

Because the lower strings, often performing in tandem with the brass, are crucial to "Heldenleben's" overwhelming sonorities, cellos switched places with violas, to the stage's front; the improvement was considerable.

Practically every first-chair player has a solo in "Heldenleben." The concertmaster's passages, though, sometimes become the central event -- especially when played with the eloquence William Steck brought to them last night. Edwin Thayer's important first horn was almost as good.

"Ein Heldenleben" was not the only work last night, though it ended the evening and could hardly help but dominate it.

Tilson Thomas opened with one of the least often played of the great symphonies, Mozart's delectable No. 34 in C major, K. 338. Full of e'lan, it is also full of grace and luster. Last night's playing was notable for delicate inflections and continuity of lines. Balances were lovely, despite the large string section (Mozart intended a large one). Ensemble should become neater at certain places in the repeat performances. And, especially for an orchestra that does not have a history of great distinction in Mozart, it was a fine accomplishment.

And, to add to the program's riches, there was also one of Tilson Thomas' specialites, Carl Ruggles' "Men and Mountains," a terse work of remarkable power by the late New England composer. It never fails to amaze how Ruggles could fold such a range of expression into three such short movements, in which the frequent silences speak almost as eloquently as the blazing climaxes.

Michael Tilson Thomas will repeat the program three times, including tonight, Saturday night and Tuesday night. As to the farther future, he should become a regular visitor with the National Symphony.