A Yankee Family Reduced for Clearance : THE HOUSEGUEST <i> by Thomas Berger (Little, Brown: $16.95; 248 pp.) </i>

He moved in without an invitation and promptly began cooking gourmet meals. He then made a move on his hostess, Audrey Graves, and also stole a pile of her cashmere sweaters. He made another move, perhaps rape, on Audrey’s daughter-in-law, Lydia Graves. He extorted money from his host, Douglass D. B. Graves. He called Douglass’ son, Bobby, a virtual idiot.

Well, all the Graves are virtual idiots, the ineffectual descendants of a once-rich, once-proud strain. Douglass goes to the family law firm out of habit--and in order to escape the folks at home. A player rather than a patriarch, Douglass has been more intimate with teen-age girls than he has been close to Bobby, his own son. Audrey compensates for Douglass’ infidelities by keeping company with several vodka bottles stashed around the house. Bobby, lazy, newly wed, was beginning to think he’d married a madwoman. And Lydia, Bobby’s wife, untainted by Graves’ blood, was indeed the one who decided she had to get rid of the guest, Chuck Burgoyne.

This is madness, to be sure, attempting mayhem on a guest who won’t go away.

Burgoyne is often evil, to be sure, trespassing on other lives, packing a pistol and daring his hosts to resist.

Burgoyne and the Graves family are right in the Thomas Berger tradition of kitchen cookery, crookery and domestic violence. The author of “The Feud,” “Reinhart’s Women” and “Neighbors” delights in crazed characters who only seem to bathe in the American mainstream. Like flawed bath towels, the irregular Graves are reduced for clearance in an otherwise regular universe. Or, perhaps more likely, Berger is trying to show us that everyone has a flaw, hidden in public, but obvious in the confines of the home and the context of domestic trouble.

So here is the upper class summering on a little island off Long Island, as usual--as ever. For a time, Burgoyne is the perfect addition; he is a presence, a man of action around the house, a novelty for a family so accustomed to going separate ways. He even saves Lydia from drowning before he turns menace and threatens the members of the household, verbally, sexually, physically.

His peril in the parlor is what finally unites Douglass, Audrey, Lydia and Bobby. They come together with something in common--the need to connive a killing.

As their plot thickens, they discover that Burgoyne belongs to his own clan, the despicable Finches who run the island on a year-round basis. Finches are the local law enforcers, the resident merchants and the domestic day-workers who keep house for the summer crowd. A lower order, the Finch family, but powerful. They are attuned to violence, and they outnumber polite society.

“Do you realize what this is beginning to sound like?” Douglass asks Audrey. “That the Finches are beginning to make their move. After all these years! For example . . . the phone service is off all over the island, not just here. Maybe there’s a Chuck in everybody’s house; we all use the Finches for everything.”

The downstairs does not revolt against the upstairs across the whole island but warfare does follow, class warfare and slapstick warfare at the Graves’ summer house. Berger will not take sides; the Graves are buffoons, and the Finches are burlesques of blue-collar America. Upper crust crumbles. Lower caste collapses.

Having thought they killed off the intruder, the Graves fail to bury him and eventually bury the hatchet instead. Audrey lectures Chuck: “Until you changed, you were the best guest we ever had. I don’t know why that couldn’t be enough for you. I don’t want to rub it in at this point, but it must be clear to you that ruining us, even if you had been successful, could not have done you any good in the long run. It’s people like us, who come from the outside, who keep this island alive. . . . I may be going too far, but I just think that at least the more level-headed Finches will understand why we had to do what we did, perhaps even applaud us in the end.”

I couldn’t quite applaud in the end. A lack of social message weakens a comedy of manners. While Berger needn’t preach, he does need a point of view, even a silly one. Portraying the loony dark of two societies is legitimate fun, but the reader has to be able to see in the dark.