Joe Orton's farcical satires of sexual confusion and British middle-class values--Loot, Entertaining Mr. Sloane, What the Butler Saw--have had no more fervent admirer than critic John Lahr. Here he attempts to combine academic dissections of the plays with a rather melodramatic treatment of Orton's very short life, chiefly the promiscuous London playwright's homosexual misalliance with psychotic, jealous actor Kenneth Halliwell: a 15-year quasi-domestic nightmare that ended in 1967 with murder and suicide. Alternating flashbacks with flash-forwards and drawing extensively on Orton's pornographic diary, Lahr extracts considerable suspense and pathos from the see-saw, love-hate relationship of ill-bred Orton and well-bred Halliwell--the reversal in their fortunes and roles, Orton's doomed attempts ""to extricate himself honorably from Halliwell's yapping misery."" But when Lahr relates Orton's sordid private life to his plays, there's often a sense of strain and more than a hint of pathology glorified: examining Orton's compulsive need for pick-up sex with ""rough trade"" in public rest rooms, Lahr intones, ""The lavatories. . . confirmed his sense of human suffering and outrageousness."" And, most crucially, Lahr's fevered partisanship simply doesn't make a convincing case for Orton as a literary figure of unique genius and major importance (none of the plays has triumphed in the U.S.); the scripts aren't flattered by Lahr's excerpts or scene-by-scene analyses, and most readers will only be made wary when Orton describes the What the Butler Saw finale--""the phallus of Sir Winston Churchill"" is waved over the proceedings ""like a magic wand""--and calls it ""perhaps the purest expression of the antic spirit in modern theatre."" Thus, the cultish pursuit of each Ortonian detail (""I remember once Joe couldn't finish his plate of food and scraped ii under a bush in the garden"") never quite seems warranted. Still, even if Orton is slightly less than the ""modern Feste"" that Lahr claims, his story has its grim fascinations, and it's all here, impressively researched and vividly dramatized; just keep in mind that Lahr is a man with a mission and not the most objective of observers.