As Milos Forman's movie version of "Ragtime" makes its picturesque but tedious way across the screen, you're reminded that certain prestige best sellers are best put out to pasture if they can't be filmed promptly. In the case of E.L. Doctorow's "Ragtime," the literary conversation piece of summer, 1975, "promptly" probably meant 1976 at the latest. Even then the book's "moment" may have passed, replaced by a climate of opinion less attuned to an epic White Liberal Guilt Trip cunningly set among real and fictional characters in the first decade of the 20th century but emotionally indebted to and limited by the countercultural pieties of the late 1960s and early 1970s.

Director Forman and screenwriter Michael Weller have adapted the novel with consistent, literal-minded solemnity. It might have been more entertaining as a mishmash. All the playful episodes involving historical figures like Emma Goldman, Henry Ford and J.P. Morgan have dropped out of the scenario. The filmmakers attempt to keep three parallel stories in motion at the outset:

The scandalous misadventures of showgirl Evelyn Nesbit (Elizabeth McGovern) after her jealous husband, Harry K. Thaw (Robert Joy), murders Stanford White (Norman Mailer).

The efforts of Tateh (Mandy Patinkin), a peddler of silhouette cutouts on the Lower East Side, to raise his young daughter and better his lot.

The response of a Respectable White Family in New Rochelle (husband James Olson, wife Mary Steenburgen and brother-in-law Brad Dourif) to a domestic crisis which snowballs into racial warfare.

Characters from all three settings are designed to cross paths. For example, brother-in-law gets a crush on the flightly Miss Nesbit, and the peddler and the nice lady from New Rochelle are destined to form an alliance. However, the Nesbit episode collapses in an embarrassing heap after three or four updates, and Forman loses track of the peddler for considerable stretches. The movie comes down -- with a vengeance -- to the racial angle, which found Doctorow cribbing the plot of Kleist's "Michael Kohlhaus" and giving it new emphasis by envisioning Kohlhaus as a proud Negro, Coalhouse Walker Jr. (well played, as far as the priggishness of it all permits, by Howard Rollins, a devilishly handsome newcomer), who turns into a kind of premature Black Panther.

Walker, a ragtime piano player, has abandoned a fiance, Sarah (Debbie Allen), who is sheltered by the family in New Rochelle after she desperately tries to abandon her newborn child in their garden. Desiring to make amends, Walker visits Sarah and eventually affects a reconciliation. On the eve of their marriage, he is harrassed by the local Irish bigots running the firehouse (my favorite character actor, Kenneth McMillan, gets to be head bigot). They soil and damage his new car, and Walker insists on justice. When he can't get it, he becomes the leader of a terrorist gang that raids firehouses. Eventually, the gang holes up inside the J.P. Morgan Library in New York, threatening to blow the joint up unless the authorities meet Walker's demands for justice.

By that time brother-in-law has shifted his fixation from Nesbit to Walker, becoming a kind of premature Weather Undergrounder. Disguised in blackface, he's also a member of the gang, specializing in explosive devices. Sarah has been conveniently knocked off, in ludicrous circumstances calculated to make Walker look even more justifiably alienated from a System Without Justice, although the situation is so trumped-up that it reduces her to a pathetic, expendable simpleton.

And there the movie is compelled to bog down, waiting for a resolution to the Walker insurrection that can, of course, hold no particular surprise or satisfaction, since it's already given that Walker is a noble, if misguided, fellow and the power structure that resists him a cowardly abomination. The only thing that really sustains human interest throughout this prolonged, no-win siege is an electrifying bit by Moses Gunn as Booker T. Washington, who fails to talk sense into Walker, and the arrival of James Cagney in his heavily publicized comeback role as the police commissioner, a cheerful bonus that's devalued when his apparently sensible character proves to be another Rotter at heart.

The Coalhouse Walker allegory set my teeth on edge when I was reading the novel. It doesn't gain any authenticity by being imposed laboriously on the screen. There's nothing else going on in the movie version of "Ragtime" except this farfetched chronicle of a saintly black fanatic proving his moral superiority to weasely white authority figures. What really defies explanation is the touching, out-of-it faith that allowed the filmmakers to believe they could bet a $30 million investment, Hollywood's first big-budget blaxploitation movie.