'Buffalo' is back - a dark tragicomedy starring Al Pacino; American Buffalo. Play by David Mamet. Directed by Arvin Brown. Starring Al Pacino

For a multimedia star of his generation, Al Pacino has kept in regular touch with his theatrical roots. Although he has been a film personality of rising reputation since the early 1970s, Mr. Pacino returned to the stage throughout that decade - most frequently in Boston.

More recently, he has been working with director Arvin Brown on David Mamet's prizewinning ''American Buffalo,'' which opened at New Haven's Long Wharf Theatre in 1980. It played successful Off Broadway engagements in 1981 and 1982, and has now reopened at the Booth Theatre on Broadway .

''American Buffalo'' is, in every sense of the word, a lower-depths tragicomedy. The intricate conversation piece takes place in Don's Resale Shop, a basement junkshop crammed (by designer Marjorie Bradley Kellogg) with castoff wares of every description. Proprietor Donny Dubrow (J.J. Johnston) is a secondhand dealer by trade and a crook by avocation. Having sold an American buffalo nickel for a high price to a neighborhood coin collector, Donny schemes to rob the collector with a little help from a couple of friends.

Donny's initial plans are quickly rearranged with the arrival of Walter Cole (Al Pacino), nicknamed ''Teach.'' ''Teach'' convinces Donny that young Bobby (James Hayden), the shop's drug-addicted errand boy, is unequal to the projected heist. Rather than being a crime melodrama in the conventional sense, ''American Buffalo'' is Mr. Mamet's indulgent study of three bungling burglars obsessed with the fantasy of the big strike they are totally incapable of pulling off.

''Teach'' is the most driven and also the most foulmouthed of the trio. ''Teach'' is the kind of person who can't really tell what he's thinking until the words pour out of his mouth. Mr. Pacino plays him like a man on a string - taut, voluble, and potentially violent. For ''Teach,'' obscenity is a way of speech, just as planning ''jobs'' is a way of life. Indeed, no small part of Mr. Mamet's comic view is to have Donny and ''Teach'' discuss the details of their conspiracy as if it were an ordinary business venture.

As an acting piece, the strengths of ''American Buffalo'' are its word patterns, cadences, and rhythms; its verbal flights, odd turns, and sudden stops. The play's antic quality derives from such scenes as the one in which ''Teach'' and Donny consult a coin directory as large as a telephone book so that ''Teach'' may learn which coins to steal.

Reviewing Mr. Brown's production on the occasion of its 1981 Off Broadway opening, my colleague, David Sterritt, described ''American Buffalo'' as ''A Fugue for Three Voices in a Junk Shop.'' That is how it is acted at the Booth. In a recent Daily News interview, Mr. Mamet said he wanted it to be about ''three guys trying to be excellent.'' To which Mr. Brown added: ''That's what we've sort of done. For them, life is infinitely possible. That's where both the humor and the sadness of the piece comes from, their perennial optimism and belief that you can bull ok your way through anything.''

The problem with ''American Buffalo'' for this reviewer is that the pathos never really catches up with the ludicrousness of the basic situation - funny as that can sometimes be. But with Mr. Pacino's eccentric jumpiness, Mr. Johnston's authoritative delivery of Donny's platitudes and cliches, and Mr. Hayden's handling of the pathetically inept Bobby's incoherent thoughts and uncompleted sentences, Mr. Mamet has been well served.

After closing here on Dec. 17, ''American Buffalo'' will begin touring in San Francisco on Dec. 27. Thereafter, the producers hope to take the production to Boston, Chicago, and London.