Stephen Metcalfe's "Half a Lifetime" (Sunday at 8 on HBO's Showcase '86) begins as a weekly poker game in a half-finished basement rec room, where four friends since school days share laughs over beer and chili, airing their gripes and renewing their dreams.

Two of them, Bart Winninger and Sam Spalding, arrive on time at the home of Toby (Nick Mancuso), a high school teacher. Bart (Gary Busey) drives a 250 cc Honda motorcycle ("You look like a bear riding a roller skate") and still works in the machine shop where he has labored ever since he married his pregnant high school girl friend. Bored and frustrated, he's nostalgic for the glory and camaraderie of high school athletics ("I miss hitting people . . . I miss the contact . . . Sometimes I want to kill somebody"), and dreams of chucking his job and moving to the backwoods of Vermont.

Sam Spalding (Saul Rubinek), the insurance salesman, dotes on his twin daughters and would like nothing better than to go to Las Vegas to gamble. He thinks he'd win; the others know he'd lose -- he's not lucky, like the fourth member of the group, "lucky J.J."

While waiting for J.J. (Keith Carradine), the other three horse around, complaining about their wives (Bart revels in "tag team wrestling . . . We have a noisy house, y'know?") and their kids (Sam changes his twins' diapers and already worries about coping with their adolescence). They rib cigar-smoking Bart about his weight, and he responds, "The muscle's still here -- it's just hiding under beer and hoagies."

Occasionally they acknowledge that the clock is ticking: "You're in your 30s -- that's half a lifetime," says Bart. "The best half's comin' up," offers another. "I don't know," muses Bart, nostalgic for his high school football days, "I don't know." He tips his hand when he comments, "It's a bitch growing up." Unwilling to admit that maybe they won't achieve what they hoped, that they might have to give up the dreams that help them live their ordinary lives, they learn that the tardy J.J. has been eavesdropping from the garage.

As the poker game finally commences, J.J., a policeman, begins: "First I want everyone's opinion on something." He relates a recent conversation with a driver he'd pulled over for speeding. The man, owner of an expensive Mercedes, said he used to have money worries, but was now happy because he had plenty: He'd stolen it, he told the flabbergasted cop.

Now J.J. offers a proposal to his friends: Let's rob a bank. "It happens all the time," he says, "all the time." We've lived half a lifetime, he points out to his startled pals, and what have we got? Nothing. We'll still have medical bills and car insurance to pay all our lives. If we had the money, he reasons, Sam could go to Las Vegas and gamble, and even if he lost it, he wouldn't be robbing his daughters of their future education. Bart could get his place in Vermont, even though his wife Valerie would never go. And Toby could have the one thing he and his wife want: a child. You could buy a kid, says J.J. It's illegal, but it happens.

Only Toby seems appalled at the idea; the others consider the possibilities as the poker game resumes, awkwardly. J.J. retreats to brood; the others deal and play his hand anyway. The mood has changed, the camaraderie stifled by tension. Ironically, when Sam thinks he has finally won at poker, they turn over J.J.'s hand and discover that he is still the lucky one of the group. Not until then does he breaks down and admit that his wife has left him. "I don't know what to do. I don't know where to go," he sobs.

Suddenly all three recognize J.J.'s loss as their own. Where to go and what to do at the half-way point in life, when dreams are dying fast. Thoreau was probably right: Most men do lead lives of quiet desperation. At least those lives are a little easier with friends who understand. Gary Busey as Bart Winninger, who wonders if his best days are behind him.