"THE ILLUSION of rescue is the mini-tragedy of my life," says Alfred, narrator of this story and tennis-playing lush of a son in whom it appears the proud New England Meriwether family has finally gone to bottom-seed.

But sometimes illusions and dreams are not as deceiving as appearances. It may take a while for the average reader, steeped in the pious alienations of the modern novel, to tumble on the fact that the source of danger is not the dusty premises and values of ancient, upper-crust gentility, but that breath of fresh air, Winston Bingham, who ultimately threatens to blow them all away. Still, rescue is possible, after all, and it is the apparently ineffectual, end- of-the-line Alfred who pulls it off.

Bingham is an unpedigreed foundling and retired basketball star on the lookout for a bigger game. As the fianc,e of Alfred's sister Dorothy, he fast-breaks into the stuffy courts of the Old Guard with his electric green suit, shoes that "may have been a petroleum derivative," and an endearing air of buffoonery.

Milburn describes the encounter in some of the most amusing passages of this delightful first novel. Alfred's father, whose law firm "bore the imprint of his aggressive pursuit of reticence," was "the ashen color of overwork, his head and shoulders were stooped. The whole thrust of his body was floorward. Only his suspenders and gold watch chain kept him propped up to the straight and vertical. I winced with sympathy for him." Elsewhere Alfred speculates, "I always suspected that my father had spent most of his life in constant fear that nameless barbarian-Philistine invaders would suddenly sweep down upon him. The invaders would destroy all his edifices of routine and civility. . . . Plunge his careful world into chaos. . . . Now the invader had arrived. . . . I pictured Dad wringing his hands and whispering over and over, 'It could have been worse. It could have been worse.' "

Alfred's mother was more aware of the dramatic possibilities: she "held out her wineglass the way Camille might hold out a hand for a pulse-check. I filled it and she brought the quavering liquid to her exhausted lips. Then she set the glass down again with trembles and poignant exhalations."

But Bingham turns out to be more than a laughing matter, and both narrator and story sober up as "the brute force of his malevolent appetites" develops. Alfred stands by helplessly as his brother manipulates the contentedly somnolent family law firm into the unwelcome vitality of a business merger. This provides Bingham with a springboard to an under-secretaryship of the Navy in Washington ("Alfred, it's a world of Lilliputians down there"), where he gets "involved" with nuclear capability, and perfectly positioned for a run at loftier positions, perhaps even the loftiest.

Meanwhile, Alfred finds his own strengths. He licks liquor and rebuilds his ailing marriage. Nevertheless, it's a tribute to Milburn's novelistic skill that Alfred's dramatic rescue of his own old-fashioned fantasy of innocent beauty (thus vindicating the Meriwether way of life for a few years at least) comes first as a surprise. Accustomed still to thinking of Alfred as the futile nonentity of his youth, the reader makes Bingham's mistake of underestimating him, only slowly, appreciatively, coming to see that, while Bingham was rising in the world, Alfred was growing up.

It is evident that Milburn has bitten off less than he can chew. I'm no lover of behemoth books but The Interloper is perhaps too short, too coarsely textured, missing chunks of the action about which some readers might like to know more. For instance, it was fine by me, but against the revealed word of current literary fashion to pass over in silence almost all the intimate details of adulteries and marital couplings, for it is a shibboleth of our time that purpose, vitality, and moral character cannot be portrayed without Significant Sex. A much greater loss is more information to flesh out some of the characters, including Alfred himself. Also, the cheeky compassion and attention to detail of the first 60 pages falters when the old has-beens shuffle off the stage, and the passage of time picks up.

Nevertheless, the book is a charmer. In the jacket copy, Milburn is compared to Cheever, O'Hara and Marquand, the kind of puff that tends to inhibit freedom and increase the pressure on first novelists the second time around. For the moment, just being Frank Milburn, author of The Interloper, is reason enough for pride.