In accord with its habitual high-toned, altruistic policy of offering viewers an alternative to the glossy pap of commercial networks, the Public Broadcasting Service tonight brings us the work of an obscure, struggling, penurious playwright. His name is Neil Simon, and he's enlisted a cast of complete unknowns: Marsha Mason (Mrs. Simon), Edward ("Lou Grant") Asner, Richard Chamberlain and Lee Grant.

Simon's glossy pap, in this instance, is called, "The Good Doctor," and it's purportedly "adapted from and suggested by" the early short stories of Anton Chekhov. The comedy-anthology orginally played on Broadway in 1973, but it's been refurbished for the "Great Performances" series by New York's WNET/13.

The seven sketches are knit together by the character of The Writer Chamberlain), who delivers a prologue and epilogue, wanders in and out of the stories making satirical commentary, and in four instances, also portrays major figures of the plot.

Two of the skits - "The Audition," about a young actress trying out for a Chekhov play, and "The Arrangement," about a father introducing his son to the mysteries of sex - are pure Simon. The rest take their premises and some of their lines from Chekhov, but otherwise, as Simon puts it: "I completely too off. I have changed all the endings."

He's changed much else, too. Simon's talent manifests itself in an odd way here, like a saving the pit and throwing away the fruit. He's extracted the mordancy and superficial ironies of the Russian, and discarded all the warmth, compassion and true wit.

The most pungent proof of this comes in "The Audition," in a spot that calls for Marsha Mason to enact, in turn, the trio of heroines at the finale of "The Three Sisters." It's the one honest, trenchant moment in the 90 minutes.

The production is impeccable; Conrad Susa's delicately nostalgic music is especially fine. And the acting, whenever the cast isn't laid low by Simon's irrepressible smartiness, is excellent. The play airs on Channel 26 at 9 p.m.