In 1978, a year after the late playwright-actor Larry Shue had left the area to become a member of the Milwaukee Repertory Theatre, he sent back a copy of his just-completed first play, "Grandma Duck Is Dead," to Joe Fab, whom he had worked with for several years at the Harlequin Dinner Theatre. After an unsuccessful attempt to get it produced at Arena Stage, Fab held on to the script with the intention of staging the play someday in Washington.

"Duck" will finally get its day when the So Far Theatre Company gives Shue's comedy its area premiere Thursday at the Source Theatre's Warehouse Rep, where it will run through March 16.

Although Fab had committed himself last summer to presenting "Duck" this season, he considered scrapping those plans after Shue died in a plane crash last September, concerned that there might be those who'd think he was trying to capitalize on the tragedy.

"I know this sounds corny, but I know he wouldn't want anything not to happen because of his death ," said Fab.

In the stage directions to "Grandma Duck Is Dead," which focuses on the creative silliness of four college men faced with the transition from adolescence to adulthood, Shue wrote: "Somehow, when it came time to put away child-like things, they looked around, saw that no one was watching and decided to keep theirs."

"That was the important thing between Larry and his friends and between Larry and his audiences," Fab said of Shue, whose other comedies include "The Foreigner" and "The Nerd."

"I would like to think that Larry would say, 'Sure, go ahead and buckle down a little bit, but don't forget to save some time to be silly.'

"That is a question in the play . . . and a message Larry left with me," said Fab.

"He didn't ever get as serious as a lot of people thought he should have," Fab continued. "It's definitely a memorable quality of his." Sanctuary's Social Drama

The Sanctuary Theatre launches its second full season March 26 with two one-act plays that focus on the homeless and exiled -- "Bag Lady" by Jean-Claude van Itallie and "The Orgy" by Enrique Buenaventura.

Sanctuary's season of social drama also includes "7-Faces," a dramatic musical about a young woman who suffers the loss of her infant daughter; David Hare's "Fanshen," based on William Hinton's documentary of the same name about the Chinese Cultural Revolution; and August Strindberg's "Miss Julie," a depiction of the demise of an aristocratic young woman. For ticket information call 745-3666. Auditions for Actresses

Living Stage Theatre Company, the multiracial, improvisational outreach company of Arena Stage, is looking for actresses who wish to commit their talents to youth in trouble, children, the aged, the disabled, the incarcerated and others ordinarily denied the theater experience.

Director Robert Alexander will be auditioning women (with a priority on Third World women) Feb. 24-28 by appointment only. Candidates should be able to show prepared work, including two monologues as characters, two songs (sung a cappella) and a poem. To schedule an audition call Robin Weiss at 554-9066. Odds and Ends

Tiki Davies has been named associate director of communications for the Kennedy Center. Davies, who joined the Kennedy Center in 1978, will retain her role as press representative for theater relations as well as take on expanded administrative responsibilities . . Board members Bonnie Nelson Schwartz and Harry Teter will coproduce this year's Helen Hayes Awards ceremony; Harry Bagdasian produced last year's inaugural ceremony . . .

The entertainment trade paper Variety reported last week that Gerald Schoenfeld and Bernard B. Jacobs, the top executives of the Shubert Organization, which owns 16 Broadway theaters and operates Washington's National Theatre, each earned salaries of $840,000 last year, plus bonuses of $3 million jointly over the last five years . . .

The Impossible Theater of Baltimore performs "Social Amnesia" Thursday through Saturday in the Baird Auditorium of the National Museum of Natural History . . . The American National Theater production of "Idiot's Delight" opens a five-week run Saturday at the Eisenhower Theater.