Now 84 years old and still indomitable, Michael Tippett is assured of his reputation as one of the major creative forces in 20th-century British music. But unlike his near contemporary Benjamin Britten, much of his work has not got the kind of attention due a composer of his stature and musical accessibility--especially not outside his home country. A measure of the neglect is the fact that two of his three early string quartets--written almost half a century ago--are receiving their Chicago premieres in this Lindsay String Quartet debut (sponsored by Chamber Music Chicago as part of its "International Season"). About these quartets, Tippett once acknowledged a huge debt to Beethoven: he attended religiously the fabled Beethoven cycles offered in London by the Busch Quartet. Indeed, in both the second and the third quartets--each containing at least one fugue--Tippett demonstrates a Beethovenish love for formal adventure but the rhapsodic Tudor polyphony and the exhilarating, dancing quality are all his own. The Lindsay foursome, to whom the composer dedicated his fourth quartet, are perhaps better suited than any other musicians to advocating Tippett's chamber music. Also on the bill is, logically enough, a quartet by Beethoven: the profound, heavyweight F-Major Quartet. Monday, 8 PM, Auditorium Theatre, 70 E. Congress; 242-6237 or 922-2110.