Isotope 217 [ tickets ], the laid-back Chicago improv quintet which features three members of genre-tripping rock band Tortoise [ tickets ] and cornetist Rob Mazurek, has announced a club tour of the Western U.S. starting Nov. 18.

The choice of venues for the 13-city stint puts the instrumental group in front of alt-rock and experimental-rock audiences, rather than jazz heads. According to Howard Greynolds, the publicist for the band's latest album on Thrill Jockey, ''Utonian Automatic,'' the group's booking agent tried to ''steer the band to play whatever clubs make the most sense...A lot of [rock] promoters know the band Tortoise and offer them more money than the jazz promoters'' who haven't heard of Isotope 217.

Coming out of recent weekly gigs at Chicago's Rainbo Club and the Chopin Theater, cornetist Mazurek, bassist Matt Lux, guitarist Jeff Parker, keyboardist/percussionist Dan Bitney and drummer John Herndon have developed a loose orientation to form. Though they're sometimes compared to early '70s projects by trumpeter Miles Davis or keyboardist/composer Herbie Hancock--or ''space-rock meets the Association for the Advancement of Creative Musicians''--the group isn't as intense as those predecessors and doesn't explore to an extreme the improvisational labyrinth.

The group's relaxed music is an amalgam of spacious, slower-tempo funk grooves with cornet and electric guitar improv of a palatable variety. ''Utonian Automatic'' is also characterized by sound effects and minimal electronic processing, a style which they developed after trombonist Sarah Smith had to leave the group due to severe tendonitis. They plan to bring the electronics on the road and combine it with their improvisations.

Greynolds said the Chicago improv rock scene, which gained national recognition three years ago thanks to Tortoise and Gastr del Sol [ tickets ], ''is still fresh and vital. It still hasn't hit its peak.'' As examples, he points to Mazurek and Parker's new album on Delmark, bassist Lux's participation in recent Drag City label projects, solid programming at the Empty Bottle and Hot House venues, and the recent MacArthur ''genius'' grant awarded to multi-reedist Ken Vandermark.

''Maybe because it's not New York or L.A.,'' he said, ''it still has a communal sense, and people are playing on different people's records.''

Isotope 217 will spend January and February touring Europe, and afterwards, Herndon, Bitney and Parker will make a new recording with Tortoise, to be released in the fall of 2000.