The doctor's bag for such occasions, the instant critic's press kit, was chock full of all the prescribed words studio PR men would hope to read - "enormous," "winning," "joyful" and the like - and with actors like Sidney Poitier, Bill Cosby and James Earl Jones you'd expect "A Piece of the Action" might offer up more than a few chuckles.

Yet what could have been a fast-paced, comic "French Connection" turns out to be a yawn: happy ghetto schmaltz.

"A Piece" is the tale of retired police Sgt. Joshua Burke (Jones), who cons two professional con men (Cosby and Poitier) into going straight as executives in a South Side Chicago community center for disadvantaged punks. After Poitier's past roles of inspiration (in "Lilies of the Field," "In the Heat of the Night," "Guess Who's Coming to Dinner" etc.) and Cosby's second-career plans as educator, you would, of course, expect their third film partnership to fall far on the other side of Superfly blaxploitation.

Indeed it does. Hardly a shot is fired; the only violence is one back-alley slugfest. As for sex, there are a peachy-clean peck or two on the cheek and a few lines in defense of unmarried cohabitation. Everything is so - so DANDY: All the uneducated kids learn self-respect and get jobs; the white mobster gives up, reluctantly, his dope trade on the South Side; and the good guys gallop off toward the sunset in their LTDs.

Although some critics panned previous Cosby-Poitier partnerships - "Uptown Saturday Night" and "Let's Do Again," one of 1975's top-grossing films - they became minor box-office hits, thanks largely to black, middle-class viewers. "A Piece" does not depart from those directions and there may even be some cross-over appeal, like the others, in that it's not a "kill whitey" film and offers a scoop of hope to everyone with an empty cone.

Folks may prefer "A Piece of the Action" to churchgoing, even though The Message comes across like a long-winded sermon. Every other line of Charles Blackwell's screenplay (from a Poitier notion) is a cliche of social comment off yesterday's editorial page. As director, Poitier has overindulged his social conscience.

Unfortunately, it takes more than good intentions - and a dash of laughs from three fine actors, a teary moment and a happy ending - to produce good entertainment. Had 30 minutes of the film landed on the cutting-room floor, you would not, ho-hum, know the difference.