What kind of Hollywood actor can portray Mitch Snyder? There's Mickey Rooney: "I've got it -- let's put on a fast!" Or Dustin Hoffman, carrying over from Willy Loman and the salesmanship of an agenda. Or Martin Sheen, who like Snyder, the nation's most visible and effective advocate for the homeless poor, had his life turned around by the Rev. Daniel Berrigan.

Last winter, Sheen was the choice of the CBS producers to play Snyder. The well-written and photographically accurate film -- "Samaritan: The Mitch Snyder Story" -- is to be televised tomorrow evening on CBS. A different title might have been, "Samaritan: How Mitch Socks It to the Bureaucrats."

The story line begins with Snyder confronting a dead-souled housing official about a family's eviction. It moves on to Snyder's moving other mountains of political indifference, from congressional committees to the wives of Cabinet members. It is Susan Baker, married to James Baker and one of the awakened, who prompts Snyder to say: "People are good. They'll respond once they know there's a problem."

Martin Sheen's response involved more than hiring out for another role. He is picky about his films, and refuses scripts that sanction violence. At 45, he is the Hollywood rarity of having stayed with one wife, one church and one political commitment, which is the activism of the radical left. Sheen is one of 10 children born to Catholic parents who immigrated to Dayton, Ohio, from Ireland and Spain. With roles in "Apocalypse Now," "Gandhi" and "The Execution of Private Slovik," Sheen is a high cut above being a journeyman actor but is still short of icon stardom.

During his filming at the homeless shelters and on the streets of Washington last January, I caught up with Sheen one afternoon when he wasn't needed on the set. I might as well have been talking with Snyder. The smoldering anger and self-criticism is the same in each man. The absence of guff is present also. Of Snyder, Sheen says that "he is one of a handful of people I have met in my life who I envy. He has full possession of his soul, which is all I've ever really wanted to possess in myself . . . He's a reflection of the very best part of ourselves. He has taken the Gospels at their word."

One of the few others to penetrate Sheen's spirit is Daniel Berrigan, the Jesuit priest, ex-con and defier of war states. The two met in 1981 when Sheen played the judge in "King of Prussia," a film about the trial of Berrigan and other pacifists who committed civil disobedience in the General Electric weapons plant in King of Prussia, Pa. "I was overwhelmed by him," Sheen recalled. "Since then, he has had the most powerful influence over my life -- just an awareness of what's going on, who's going on and why I'm not involved. He's made me aware of my own cowardice, as all great saints do."

Sheen is a coward? He claims to be -- by not doing enough for the poor, by not going to jail for his beliefs and for "paying my taxes and buying more bombs with them than anybody I know . . . I'm still in love with my life, my image, my money and all the things that keep us separated from God and ourselves."

To compensate -- "work off the guilt," in the language of Irish Catholics -- Sheen gave to Mother Teresa most of the $200,000 he earned from "Gandhi," and went to Nicaragua with Witnesses for Peace. The contras, he says, "are obscene assassins" and make us "surrogate murderers." Sheen has raised funds for medical aid to El Salvador.

Doing the Snyder film was part of Sheen's commitment to political activism. Others in Hollywood do that by becoming the mayor of Carmel or president of the Screen Actors Guild. Sheen confessed to having had doubts about the usefulness of the Snyder film. "The danger in making this movie," he told an interviewer, "is that it will be too sentimental. With no political premise, the film will look like the story of a bunch of sorry do-gooders."

Politics is in the film, though nothing to unsettle anyone. Snyder's most recent fast is omitted, when he again starved himself to the brink of death to pressure the Reagan administration to fulfil its promise to turn the shelter run by Snyder's Community for Creative Non-Violence into a "model" facility. It is likely the film will help bring money to the shelter and Snyder's group. Their two-story building, in which scenes were shot and the poor recruited as paid extras, costs $12,000 a month to operate. Most of that is for utilities. Staffing is volunteered by CCNV and guests at the shelter. No government money is accepted or sought for the work.

The full story of Snyder's politics and his rages against the mistreatment of the destitute awaits telling. Let it be called "Samaritan II."