Breaking up is hard to do, but staying together can be murder. A four-hour ABC movie airing in two parts, tonight and Friday at 9 on Channel 7, explores both these alternatives and a good deal more besides. "Breaking Up is Hard to Do" is almost impossible to leave once you've started watching, because it has strength, veracity and a critical case of the smarts.

The film, written by James Henerson and, according to ABC, "inspired by a true incident," finds six aging L.A. buddy-boys going through that great American institution known as Marital Difficulties. So they band together for a summer of moderately wanton weekends at a Malibu beach house, the idea being to booze the blues away and forget about the serious entanglements of heart and mind that have so successfully screwed them up.

Naturally this plan goes awry as the League of Nations and before long, frisbee-tossing and beer-belting turn into fist-fighting and true confessions, sobs, tears and rites of recrimination. And the way these things develop, in Henderson's script and thanks to an exceptional cast, is with a persuasive naturalism and an unusual forcefulness.

The tendency in TV movies about social problems is to generalize them into innocuousness, sometimes almost into abstraction. Even with this picture, ABC is essentially saying to the viewer, "Here is our movie about how divorce affects the injured male." To their credit, Henerson and director Lou Antionio gave ABC a better movie than it may have expected. They beat the rap of tidy oversimplification with characters that are thoroughly out and full of life and guilt.

Robert Conrad (Mr. "I Dare you"), Bill Crystal (of "Soap"), Jeff Conaway (of "Taxi"), Tony Musante (once "Toma"), Ted Bessell (of "That Girl") and David Ogden Stiers (of M*A*S*H") play the six strained pals, and they are all of them first class in their roles.

The women in their lives, well cast and played without affection, contribute forthright and realistic complications, especially Janice Karman as Beth, with her agreeably Keatonesque giggle (that's Diane, not Buster) and Susan Sullivan as the lofty and chilly Diane, who leads Conway to, but not quite up, a primrose path. These people are not monsters or saints; we are CAPTION: Picture, In "Breaking Up Is Hard To Do," from left, standing Billy Crystal, Tony Musante, David Ogden Stiers and Jeff Conaway; kneeling: Ted Bessell and Robert Conrad given all the evidence we need to evaluate their plights and appreciate their motives.

Of course, like most TV movies, this one is padded out with extraneous physical action (a romp on motorcycles, a brawl in a bar and more than a handful of '70s cliches ("I know what you're going through; I've been there").At times, too, it reduces complexities to the level of trendy topics on the Phil Donahue show, with the implicit prescription that everything will be fine if people can get "in touch with their feelings" and learn how to handle their "pain." Caring, sharing -- blah blah blah.

And yet the glibness tends to be minimal. Easy answers do not pour out like syrup, and shortcomings are repeatedly redeemed with quick, trenchant little events, like Steirs crying in his car after his wife has thrown him out, or, much later, doing a full facial collapse when he sees, from a distance, another man in his house holding his kid, standing in his doorway with his wife.

Bessell, who has grown as an actor, plays a man stricken with a form of cancer that leaves large and unsightly scars on various parts of his body. He won't date women, for fear they will be repelled by the sight of him, but a restaurant randezvous with Karman as Beth ends with an inspired portentous fade-out. He tells her his sob story and her response is an exquisitely succinct invitation to her house: "Are you allergic to cats?"

The terminally ill hell-raiser has become something of a melodramatic cliche, but Bessell gives it new validity, and Henerson allowed him at least one burst of terse eloquence on the subject. "I'm going to die, and soon," he says, "but I'm going to be flying when it comes and they're going to have to shoot me out of the sky."

Even Conrad, usually a caricature, shines here, because the man he plays is a good-time bully on the outside with an open wound of nasty secrets and self doubts on the inside; when Conrad exposes that, it may be all the more effective because he's played such one-note stiffs in the past. And Musante, perennially underrated as an actor, has his finest moment when he is, to his poignant disbelief, actually turned down by a girl on whom he has lavished what heretofore served as all-conquering masculine charm.

Perhaps the most formidable trick being pulled off here is a central problem facing all dramatists: exhibiting characters who may behave stupidly or despicably and eliciting in us not contempt but unnerving recognition. When Musante, in anger and disappointment, slams a door over and over and over, you don't think, "How dumb." You think, "Oh yes -- that reminds me of the time . . . "

"Breaking Up Is Hard To Do." May lack breakneck narrative momentum -- it is essentially a diary kept by a camera -- but momentum doesn't matter much in TV movies, since whatever accrues will be broken by the next commercial break anyway. Perhaps all the more impressively for that very reason, "Breaking Up Is Hard To Do" proves genuinely hard to shrug off.We see what the boys in the beach house will do, and we realize we might do the same.