If you noticed patrons fanning themselves during Tuesday's concert by the Kronos Quartet, it wasn't just the temperature of the building, the Musuem of Fine Arts. There was also a lot of heat onstage, most of it generated by the performers.

I won't deny the special lighting may have played a part. But in its way the musicmaking was no less electric, in both presentation and content.For almost uniquely among contemporary chamber groups, Kronos has virtually created its own repertoire. They may or may not be alone in performing pop-style in leather jackets and open collars (not to mention first violinist David Harrington's tinted shades). Where they are definitely alone is the music they play, an intriguing blend of such ultramodern voices as Philip Glass and Ben Johnston, their own commissions from the likes of Kevin Volans and Astor Piazzolla (he of the innumerable tangos) and a sprinkling of jazz and even pop arrangements again, mostly specially commissioned.

Tuesday they did include one "standard," the String Quartet No. 4 of Hungarian composer Bela Bartok, written in 1928 by Kronos standards, eons ago. And I must say it was performed with a special intensity, not diminished by the subtlety of the playing.

Thus the knotty first movement was laid before us with lyricism and logic even early on one could feel the blocks a-building. Followed by an eerily muted second movement (for my taste a bit less than Prestissimo) and a "night music" which after a hushed beginning gradually took on added strength and definition.

Similarly the subdued pizzicati of the fourth movement were registered in such a way that individual chords seemed to jump out like skeletons. And although the finale had both bite and acerbity, one was still aware of the richness of Joan Jeanrenaud's cello. Otherwise the standout for me in this remarkable foursome was second violinist John Sherba, whose strength and beauty of phrasing were apparent even in the less familiar pieces on the program.

Not that they should be less familiar. Witness the sparks churned up by Australian composer Peter Sculthorpe's Quartet No. 8, its "rice-pounding" music making use of as many exotic bowing techniques as the Bartok. By the same token Glass' "Company" finds him at close to his best, its quiet economy concealing a wealth of detail behind the supposed minimalist austerity.

However, neither of these made a more favorable impression than the piece that opened the evening, Ben Johnston's Quartet No. 4, subtitled "Amazing Grace," an 11-minute set of variations on that tune that sounds almost like Vaughan Williams' "Dives and Lazarus" Variants as they might have been done by Charles Ives or, in places, even Harry Partch. Certainly the music itself falls easily on the ear and here it was performed with feeling, sensitivity and sterling ensemble e.g., the beautifully integrated counter-rhythms of the middle variations.

Kevin Volans' "White Man Sleeps" No. 1, the first of five such pieces, falls somewhere between the Glass and the Sculthorpe in its repetitive aspects and ethnic derivations. (The title comes from a Nyangan panpipe dance performed so as not to wake the sleeping landowner.) Interestingly, the more subdued it gets the more affecting it becomes.

Ditto the nocturnal musings of Tom Darter's arrangement of Thelonius Monk's "Round Midnight," with its deceptively simply melodic contours. Here Harrington was the leading voice, as he was in another Darter arrangement, of jazz great Bill Evans' "RE: Person I Knew."

Finishing off the first half was Piazzolla's "Four, for Tango," a Kronos commission I found more interesting in execution than conception. But Steve Riffkin's arrangement of Jimi Hendrix's "Purple Haze" (practically the Kronos' signature tune) can still raise a few hackles, as it did as an encore intense, indulgent and, like nearly everything else on this program, exciting.