When buffoons ruled the Great White Way; The Great Clowns of Broadway, by Stanley Green. New York: Oxford University Press. 247 pp. $19.95.

In his excellent new book, theater historian Stanley Green provides more than just a nostalgic excursion down memory lane and the Great White Way. In addition to its lively descriptions and analyses of styles and methods, ''The Great Clowns of Broadway'' offers biographical information, samples typical routines and dialogue drolleries, and quotes extensively from critical opinion of the period.

The overall result commemorates and evaluates the contributions made by these fabulous funnymen and funnywomen to a uniquely American entertainment form in one of its most creative periods. Mr. Green's chosen clowns flourished from the mid-1920s to the early 1940s.

He writes:

''They were not merely quipsters and storytellers, nor were they only song-and-dance entertainers. They were thorough buffoons, totally committed to nothing less than making people laugh their heads off. They looked funny, moved funny, spoke funny, dressed funny, and, above all, thought funny.

''They didn't portray comic characters, they were comic characters. And they were as vital to the very existence of the shows in which they appeared as were the breezy juveniles, the perky heroines, the powerhouse song belters, or the high-stepping chorus.''

Mr. Green deftly captures the individual characteristics of his comic artists. For instance, Fanny Brice was ''an imp, a madcap, an uninhibited force'' who ''mocked the artistic pretensions of ballet dancers (pronounced 'belly densehs') and the excesses of sirens of the screen or of history or literature.''

Beatrice Lillie, the other female member of this clown pantheon, ''remained preeminent in her ability to apply slapstick with a regal hand.. . . Miss Lillie , above all other clowns, understood and practiced the comic art of detachment.''

Goggled Bobby Clark was ''nothing less than the embodiment of the Broadway clown . . . the hayseed rogue with a face that shone with beaming good nature.'' Joe Cook, with his verbal nonsense and Rube Goldberg inventions, was ''bland, cheerful, brash, ingratiating, glib, amiable, breezy.'' Multitalented Ed Wynn, the bespectacled ''perfect fool,'' was ''the disarming and amiable busybody. . . .''

One of the sweetest of Broadway's major clowns, ''Jimmy Durante was the most frenzied, the most uncontrollable, and . . . to use a Durante-coined word - the most exibilant.'' The lovable Victor Moore was ''Broadway's most endearing, wistful, pathetic, and gullible clown.'' Of the comedians who had to deal with life's unending problems, ''W. C. Fields projected as expertly . . . as any performer who ever extracted humor from adversity . . . a character continually at the mercy of unmanageable forces.'' Willie Howard's ''stoop-shouldered stance and worried expression gave him the appearance of a perpetually confused little man buffeted by countless injustices.''

Mr. Green confirms certain popular notions about clowns and refutes others. It appears that all comics are serious, and all, to a greater or lesser degree, are worriers. However, with respect to the assumption that buffoons invariably yearn to play serious drama, he comments: ''A comic learns early on what he can best do on the stage, and he usually spends the rest of his career perfecting his art.''

Nevertheless, some of the great clowns in his chronicle did succeed in dramatic parts. Bert Lahr was an inspired Estragon in Samuel Beckett's ''Waiting for Godot.'' Ed Wynn, at 69, rebounded from a low point in his career with memorable dramatic roles in the film ''The Great Man'' and TV's ''Requiem for a Heavyweight.'' Victor Moore acted in a revival of ''On Borrowed Time,'' and made a moving farewell appearance as the Starkeeper in a City Center production of ''Carousel.'' On the lighter side, Bobby Clark was larkish in Congreve's ''Love for Love,'' Sheridan's ''The Rivals,'' and Moliere's ''The Would-be Gentleman.'' W. C. Fields was an eminent movie Micawber.

Mr. Green takes due note of his great clowns' cavortings for film, radio, and television audiences. But he insists that all great comedians belong to the theater. The book's goodly selection of photos and more than 40 pages of credits confirm the view.

He recalls the ''deal'' Fanny Brice said she made with the audience every time she went on stage: ''I look at them, I smile at them, and I tell them - and by looking at me they know - that this is really a private party. It's just between them and me.''