Irakere, whih opened the Stephen Stills concert last night at Constitution Hall. gave the audience an interesting preview of what was to follow.

An 11-piece Afro-Cuban jazz unit which returned with Stills from the recent rock junket to Havana, Irakere is a cauldron of polyrhythms, shifting meters and a blasting brass ensemble. The snake-charming soprano sax, by Patuito D'Rivera, had the crowd standing, and before long the audience, obviously predisposed to rock, was chanting out words in a foreign tongue.

When the lights came up, Stills was fronting a group of the same size where percussionists stood six deep. Latin rhythms have always punctuated his work, and last night he let loose with darkly textured versions of "For What It's Worth" and "Cuba al Fin," the latter sung in Spanish.

His "Who Do You Love" juxtaposed Jimi Hendrix and Bo Diddley, while he strutted around the stage in a modified Chuck Berry strut. When he tired, Bonnie Bramlett took over vocals and turned in an R&B version of "Love the One You're With."

There is good reason to be leery of Stills' solo work -- his last album was just an aimless excursion that covered too much territory in too little time. But last night gave him a chance to break away from the confines of Nashand Crosby harmonies.