As listeners sat in Wolf Trap's Meadow Center last night sweating and fanning themselves, circumstances did not bode well for the Cleveland Orchestra's concert about to begin. The weather was like a Dog Day in Delhi.

But the Cleveland is one of the world's pre-eminent orchestras. And if any ensemble could salvage the evening, they could--up there on the makeshift stage, which lacked any cross-ventilation, with their coats off and their collars open.

As it turned out, though, the performance, under the Mexican conductor Eduardo Mata, who himself donned his coat, was never less than splendid and was on occasion quite brilliant.

The Cleveland is traditionally America's most distinguished Mozart orchestra, thanks to 25 years under George Szell. Last night it played the Clarinet Concerto, with first clarinetist Franklin Cohen. All three movements were finely balanced and phrased, with the winds, especially, at their most expansive.

Cohen, whose tone is large and smooth, played the first movement so suavely that it lost a bit of its vitality. Then came the reverential serenity of the slow movement--which sets a poignant mood for what would turn out to be the composer's last concerto. Cohen played it slowly and softly--in other words, the hard way--and it was very touching. The finale was fast, bristling with life. Mata's conducting was exemplary.

The last work was the monumental Copland Third Symphony, with its rough-edged majesty. The first two movments got off to a somewhat lax start, and one concluded that the heat was such that the players were simply exhausted.

Then as the free-form third movement took shape, a real sense of musical atmosphere took hold. The dreamy, almost impressionistic passage near the end was exquisite. It set up the music superbly for the bold, noble fanfare in winds, brass and percussion that blazes out next (this is the famous section better known as the "'Fanfare for the Common Man"). It was stunningly performed. Rhythms were precisely on the beat. Sonorities were magnificent. And ensemble was impeccable, except for a miss or two in the horns (which were placed in an area where the temperature must have been in the mid-90s by that point in the evening).

Then Mata set a very brisk pace for the finale, with remarkably exact articulation in the strings. The bracing accents and cross-rhythms were precisely on the mark. This movement is one of Copland's grandest creations, and one cannot recall hearing a more incisve performance.

Last night's weather would have given most orchestras sufficient excuse just to plod through the concert. But not the Cleveland. That's what separates the great orchestras from the merely good ones.