AFTER SEVEN YEARS of recording and touring, Gentle Giant, the English "classical-rock" group, has apparently had a professional change of mind. Or at least half of one. Their newest record, The Missing Piece (Capitol ST 11696) is, literally, a half-hearted attempt at the commercial market, with side one featuring short, basic pieces, while side two continues with their former style of complex and classically derived composition and playing.

The results, as one might expect, are mixed. Side one suffers from a lack of commitment musically, and from an awkwardness of form that suggests that, whether they like it or not, Gentle Giant is not a commercially oriented group. "Who Do You Think You Are" and "Two Weeks in Spain" are melodically interesting but hardly memorable. "Betcha Though We Couldn't Do It" is a disaster-this attempt at "rock 'n roll" is as much a mockery of high quality hard rock as it is of Gentle Giant's confidence in their own musical identity. They are not a group of basic rockers and they should know it by now.

Side two returns to the estabished Gentle Giant style of rich vocal and instrumental harmonies and technically complex musical sections. The four pieces comprising this side blend elements of Renaissance and Baroque music with rock, producing a music that is eclectic and lyrically engaging. More importantly, there is an honesty of expression to these pieces that comes about only when musicians enjoy and respect what they are playing.

Despite their lack of commercial success in the past, Gentle Giant has always displayed taste and imagination in the music they create. The Missing Piece represents a partial departure, and one that should be temporary, from the standards that they have previously maintained in their music.