By WALTER GOODMAN

COMMIES

A Journey Through the Old Left, the New Left and the Leftover Left.

By Ronald Radosh.

Illustrated. 216 pp. San Francisco:

Encounter Books. $24.95.



or most of his youth, beginning at least at the age of 18 months, when, in a stroller, he was propelled along the yearly Communist Party parade down Fifth Avenue, Ronald Radosh was a poster boy for immigrant radicalism. So he reports in ''Commies,'' an account of his adherence to the left-wing faith into which he was born (he describes his father, a milliner, as a classic front man for a Communist Party instrument called the Trade Union Unity League) and which he did not shake off until middle age.

Radosh seems to have been an exemplary son, throwing himself fervently into every cause that bore the party's sometimes shifting stamp of approval, singing along with Pete Seeger, attending a party-inspired summer camp and a New York City red-diaper high school (known jocularly as ''the Little Red Schoolhouse for little Reds''), handing out petitions as required and participating in youth festivals modeled on Soviet extravaganzas. The party was never known for its humorous side, but it did have one permitted joke: ''What Jewish holidays do you celebrate?'' ''Paul Robeson's birthday and May Day.''

No doubt there were some left-wing organizations that Radosh managed not to join in his college and postgraduate years, but that seems to have been owing to inadvertence, not premature disillusion. When, in 1956, Soviet tanks rolled into Hungary and some partyniks called it quits, Radosh joined the Communist Party USA as a full-fledged member. He and his new wife celebrated their marriage by watching the annual Labor Day parade. His bouncing around from the Old Left to the New Left and its many offshoots does not make for consistently exhilarating reading; it takes some dedication to sort out one group from another, since they all seemed to be using ''socialist'' in their titles. But when he refers to the left's ''reflexive hatred of the American system,'' he knows whereof he writes.

His encounters with Tom Hayden, Staughton Lynd, Herbert Marcuse, Abbie Hoffman and other celebrities of the anti-Vietnam War left bring back the heady days of 60's protest, but by then Radosh, earnest as ever, was questioning his faith. In one of his stuffier sentences, he describes his growing doubts about the whole gang: ''As a young man of vast intellectual curiosity, I was beginning to discern the true face of Stalinism.''

For one of vast intellectual curiosity, he reveals himself to be a slow learner. Among other influences that helped Radosh to free himself from the left was the breakup of his marriage: his wife, in search of a middle-aged cause, was converted to a faith in consciousness-raising that required the smashing of monogamy. Happily, he found other available women and so ''rehabilitated the sexual self-esteem that my former wife had crushed.'' It sounds about as much fun as watching a Labor Day parade.

It was the Rosenberg case that at length liberated Radosh from the left-wing ambience. ''The Rosenberg File,'' the 1983 book he wrote with Joyce Milton, was a persuasive argument, except among the truest believers, for Julius's guilt and Ethel's likely implication. Here, Radosh takes the opportunity to beat up on many old pals, ''unreconstructed remnants of the Old and New Left,'' who failed to see the light. His training in invective serves him, too, against non-Stalinist leftists like Irving Howe and Michael Harrington, whom he had come to hold in esteem but who refused to join his campaign against the Rosenbergs. Referring to Harrington's rejection, Radosh writes that ''although he knew I was correct about the case, the truth had to be subordinated to his present political agenda, which was to get former Communists as his comrades.'' It dawned on Radosh that ''perhaps the left was wrong not just about the Rosenberg case, but about most everything else.''

AS the sun sank on his socialism, Radosh found himself contributing to the conservative monthly The New Criterion instead of to Irving Howe's Dissent, and charging that he was blackballed from a teaching job at George Washington University, ''where, if I had still been a Communist writing left-wing history, I probably would have breezed in.''

One understands that for Radosh, who spent so much of his life contributing to lost or unworthy causes, redemption is no joke. Yet the self-importance of the fringe players who occupy his pages does have its comical side. If he cannot recognize that, it may be because he has himself been infected by too intimate an association. Even after casting off the ideologies of the left, he can't rid himself of the personal grudges and party-line rhetoric. He ends his book with a wishful epitaph that sounds like an Old Left slogan turned inside out: ''The country is stronger for having encountered and withstood us.'' Thanks, Ron.

