As disappointments go, "True Confessions" has a lot going for it. Led by Robert De Niro and Robert Duvall as an offbeat, wary set of siblings -- respectively, a Catholic priest and a homicide detective -- the cast is the most impressive since "Brubaker." The subtle interplay between De Niro and Duvall would be sufficient to sustain interest in the movie, despite the ineffective murder plot invented by novelist and screenwriter John Gregory Dunne, who resorts to subterfuge in order to fabricate a critical turning point in the relationship between these emotionally inseparable brothers, Des and Tom Spellacy.

In addition to intriguing roles for the costars, "True Confessions" provides wonderful opportunities for two of my favorite character actors, Charles Durning and Kenneth McMillan, and an exceptional gallery of supporting stalwarts, notably Ed Flanders, Burgess Meredith, Cyril Cusack, Rose Gregorio, Jeanette Nolan and Louisa Moritz. The director, Ulu Grosbard, began to emerge as a remarkably sensitive orchestrator of realistic acting in the powerful, underrated crime melodrama "Straight Time." Opening today at area theaters, "True Confessions" confirms Grosbard's admirable concentration on the nuances of performance and setting. Moreover, he expands his range by evoking a fascinating period setting for criminal undercurrents, Los Angeles in the late '40s.

Between the splendid cast and the unsavoriness of the period details, "True Confessions" generates so much absorbing human interest and persuasive texture that the miscalculated plot seems a minor letdown. You're puzzled by Dunne's style of blundering. Despite some excessively derivative overtones from "The Godfather" and "Chinatown," Dunne appears to get something distinctive cooking in "True Confessions." The double-track exposition alternates between Duvall and McMillan as cynical, semicorrupt homicide cops investigating a gruesome murder -- the dismemberment of a young woman dubbed "The Virgin Tramp" in the yellow press -- and De Niro as the respected, astute, string-pulling chancellor of the Archdiocese of Los Angeles, obliged to strike a diplomatic balance between practicality and piety.

It's fascinating to be taken behind the scenes with both cops and priests. As the observations and the tension begin to accumulate, one anticipates a climactic convergence of the worlds in which the Spellacys operate. Presumably, it will be calculated to uncover the identity of a murderer while resolving the conflicts that simmer between the brothers. One gathers that the conflicts are left over from a Catholic childhood and that Tom, in particular, is nursing a grudge against Des as the family's Chosen One, the virtuous son singled out by a pious mother for a life in the church. Moreover, it's apparent that the Durning character, Jack Amsterdam, exacerbates the hostility. Tom despises Des for associating with Amsterdam in the financial interests of the church, and his self-righteous resentment springs from a profound awareness of personal corruption -- Amsterdam was running the vice rackets when Tom was on the vice squad, and Tom was his bagman.

The movie compresses and enhances the original novel in many respects. Superfluous characters are jettisoned. Grosbard's transparent style of directing streamlines the exposition, relieving much of the monotony imposed by Dunne's gloomy ruminations. After awhile, the characters in the book began to sound alike too, an undifferentiated chorus of embittered, sardonic sinners, beyond either consolation or salvation. The actors relieve that note of woeful monotony as well. The movie story has far more color and shading than one might imagine possible from a trek through Dunne's book.

However, it remains an anticlimactic story in the last analysis. It seems both unsporting and self-defeating of Dunne to confront us with a deliberately, even excessively shocking, murder case and then flub the identity of the killer, a character who has no bearing on the ultimate disposition of the story. McMillan's wisecrack when first observing the butchered corpse -- "The butler did it" -- might as well be a brilliant wild guess. Not that there's a butler, but for all it matters, the nonexistent butler could have done it anyway.

This misjudgment also makes it difficult to play along with a point that is supposed to matter -- Tom breaks the case publicly in a way that exposes Des to professional disgrace. But since there doesn't seem to be any case left after the killer is revealed, you're not sure what kind of scandal Tom could possibly create. Des is "implicated" in such a remote, roundabout respect that the idea of public scandal looks farfetched. Moreover, it's superfluous. The whole drift of the story suggests that Des himself has grown so disillusioned with diocesan politics that he's probably going to resign the chancellorship and find sanctuary far from the limelight, satisfying the author's notion of the only honest solution for a truly religious man. Tom's little shove is at once unbelievable and unnecessary.

It's peculiarly satisfying to see De Niro playing a controlled, intellectual personality so soon after his crazed rampage in "Raging Bull." Although he's made his strongest impression playing psychos in "Mean Streets," "Taxi Driver" and "Raging Bull," De Niro has always had a knack for smart, introspective characters. In a better movie version of "The Last Tycoon," he might have been a great Monroe Stahr; and his Vito Corleone in "The Godfather, Part II" was a brilliant fusion of his restrained and violent sides. He brings absolute conviction to Des, a fact that also weakens the plot manipulations. Watching De Niro, one feels an intuitive sympathy with Des' penetrating intelligence and self-doubts. The feelings that would lead him to renounce a prestigious career are persuasively suggested in his concentration and his dry delivery. Des is another solitary soul, but perhaps he's the most subtle and accessible solitary De Niro has yet embodied -- a man whose isolation draws you closer instead of giving you the willies.