F.I.S.T. - AMC's Carrollton 6, Bradlick, Fairfax Circle, K-B Bethesda, K-B Fine Arts, Wheaton Plaza 3.

The '30s union scenes in "F.I.S.T." are done in warm tones of brown and fire-glow; the '50s in gray and glass. The sound of the '30s is the noble union song; the sound of the '50s a tangle of evasions into Senate committee microphones.

How did we get from one to the other? Here is a film that attempts to explain it - opening while the Justice Department is telling Congress that some 300 union locals affiliated with major international organizations are "severely influenced by racketeers."

The case for Jimmy Hoffa, as it were, is not an easy one to make sympathetically. But Sylvester Stallone, as actor and, with Joe Eszterhas, writer of a script from Eszterhas' story, has at least raised questions that make it difficult to dismiss the development as a simple progression from idealism to greed.

Stallone forcefully and engagingly plays a union organizer in simple and tough days, on the side of starving workers against rich bosses. For requesting overtime and workmen's compensation, they are fired, beaten by goons and even murdered. You can't watch this happen without wishing they had some more forceful way of fighting back than passing the coffee and singing those songs.

Well, they think of one. And it's pretty much with audience consent that the F.I.S.T. in the Federation of Interstate Truckers is supplied by those who know how to fight back. It seems the only way. Then, of course, it's theunion's turn to do a favor for the gangsters - and so it goes.

It's a pure way of accounting for the metamorphsis of an idealist. The film is careful to reject any other motives: He rejects early attempts of management to buy him out when he needs it most; he rationalizes the strengthening of the union by force with the belief that it's for the good of the worker not to have the choice to abstain from the struggle; he is not excessively on the take personally and rids the union of a president who is; he keeps miraculously sheltered from seeing the dirty work; and he loves his family.

Thus while you see him go from three-piece cheap brown suits to three-piece tapered gray ones, and from the dirty kitchen to the pillared suburban house, the rise is modest enough that it's plausible that his wife still thinks of him as a courageous underdog, and even that he does, himself. After all, the worker he represents has also gone from the skinny 14-hour-a-day driver to the fat guy frolicking in a Miami pool at convention time.

The only step obviously wrong, then, is the one articulated early in the struggle by a friend and partner who steps back into local unionism when he sees what it takes to go bigtime: If they hire goons, he asks, "How are we going to tell the difference between them and us?" Yes - but then you get back to the question of how he was otherwise going to fight a combination of owners and police.

The case is not a strong one, and the film is too long, with a number of Washington scenes that are rather hockey - Rod Steiger shows an extraordinary lack of force, even for a crusading senator - but it does raise the question of how it happened that the union headquarters are now made of marble.