With Sunday night's closing "A History of the American Film," Howard Witt takes his leave of Arena Stage.

Witt will be going out with a hit in which he zips through eight parts, pushing his nine-year total to 47 roles. Aptly, Witt's present assignments, ranging from Uncle Sam to Director Von Leffing and six quickie roles, reflect the variety which has distinguished his Arena acting career. Gogo in "Waiting for Godot," Mangan in "Heartbreak House," the Inspector in "Madness of God" and Managing Editor Burns of "The Front Page" as well as "Doctor Faustus" at Washington Cathedral and major parts in the Soviet Union tour with "Our Town" and "Inherit the Wind" show a striking range of professional versatility.

Witt's new base will be Los Angeles, so count on catching him on screens large and small.

The Folger Theater Group's "A Midsummer Night's Dream" has extended its run through July 10. Next season will begin with "Teeth 'n' Smiles," by England's David Hare, who writes of a rock group at the end of the frantic '60s. A new American play and three by Shakespeare, chosen from "As You Like It," "The Two Gentlemen of Verona," "Hamlet," "Othello," "The Merchant of Venice" and "Richard III," will make up the season's balance. Reduced subscription rates will be available through July 31; details at 546-4000.

An Alan Ayckbourn logjam will occur July 12, when the British comedy master will have openings at Olney and the Eisenhower. First to announce was Olney with "Absurb Person Singular." Now the KenCen will preview "Absent Friends" in July 11, to open July 12 with Eli Wallach, Anne Jackson and Lee Richardson in the starring roles. Olney's run is through July 31, the Eisenhower's ends Aug. 13.

Marvin Hamlisch's benefit concert with a symphony of 70 on Saturday night in the KenCen Concert Hall amounts to a further boost for "A Chorus Line," which hardly needs it. Invitations are in the mails for a Sept. 18 benefit for Planned Parenthood of Metropolitan Washington with seats ranging from $35 to $100. Among this Saturday's vocalists will be Sandra Voris, who has an unusual How-I-Got-the-Job angle. Rehearsing her own songs in a rented studio, she was overheard by the musical director of "A Chorus Line." He introduced her to composer-conductor Hamlisch and now she appears with him in all his symphonic concerts.

"Sweet and Hot, The Songs of Harold Arlen" will be introduced at the New Playwrights' Theater Wednesday night. Director Ken Bloom and Berthe Schuchat have compiled this from the works of the sometimes overlooked Arlen, who composed such Americana as "Stormy Weather," "Somewhere Over the Rainbow" and "Paper Moon." Reservations at 232-1122.

With "Voices of Pride" ending Saturday, the Trapier's Shakespeare & Co. next Tuesday opens the first area production of "Scapino," the Frank Dunlop-Jim Dale variation on Moliere's "Scapin." Edward Crow directs for the run ending July 16, with a preview Wednesday nigth. Reservations at 686-1733.

Lady Bird Johnson, who introduced Carol Channing and "Hello Dolly!" for its fourth anniversary in the White House East Room, is scheduled to repeat that gracious gesture tonight in Houston, where the Houston Grand Opera revival, guided by composer Jerry Herman, opens at 25-city tour. Look for this at the National in January, 14th anniversary of its New York premiere. Unlike most revivals, this one will have a larger cast than the original, with Eddie Bracken as tight-fisted Horace Vandergelder. Also scheduled for tonight's Houston audience - Isabel Wilder, sister of the late Dolly creator, Thornton Wilder.