In a salute of sympathy to their director and his distant colleagues, the cast of Arena Stage's "The Lower Depths" has volunteered their services as a benefit the second night of their production, Thursday, March 31.

Romania's visiting director, Livia Cinlet, has learned that his Bulandra Theater was one of the three theaters destroyed in Bucharest's recent-earthquake. One of his company's leading performers was killed.

All proceeds from the Arena benefit will go to the aid of theater workers and their families. Tickets for the benefit will be $3.50 and can be reserved at 554-7890. Contributions to Earthquake Benefit will be received at the theater, 6th Street and Maine Avenue SW, 20024.

Another Arena special will be given Friday and Saturday at 8 p.m. and Sunday at 7:30 p.m. by its Living Stage company in the Old Vat Room. The attraction will be "Faces of Fascism," evolved by director Robert Alexander's company from Kenneth Wooden's "Weeping in the Playtime of Others: America's Incarcerated Children." Reservations at 554-9066.

"Dramathon 77" is the New Playwright's Theater's second annual nonstop 54 hours of comedy, drama and musicals starting Friday at 8:05 a.m. Full-length and one-act originals and excerpts from its earlier offerings are among the 41 events, some of which will be aired live over WGMS. The rates: $12 for a pass good all 54 hours or a daily pass for $5. Meantime, up at Joseph Papp's New York Public Theater last night, the NPT's production of "Hagar's Children" opened with its Church Street cast intact, Robert Graham Small directed the unusual drama by Ernest Joselovitz.

With a cast dominated by professional Indians, "Black Elk Speaks" opens Friday night at the Folger Theater. Christopher Sergel's play stems from the book by John G. Nelhardt and has been staged by Jonathan Alper. Reservation at 546-4000.

Brecht's"In the Jungles of Cities" opens a Thursday-Sunday nights run Friday at ASTA Theater, 612 12th St. NW, under the direction of Jay Allison. The play, inspired by what Brecht had read of Chicago, will include a new score evolved by ASTA's four-member ensemble. Reservations at 629-8368.

This year's One-Act Play Tournament, which plays this Saturday and the following Friday, is down to five entries, a very poor record for the 49th running. Once there were as many as 26 or 30 from local groups.

The reason seems to be that all announcements about it had to be cleared through the District building instead of the D.C. Department of Recreation. The first notice about the tournament reached this desk the day after the deadline closed. One entry was 10 days in the mail.

This Saturday's 8 p.m. performance at Chevy Chase Community Center will be the Silver Spring Stage in "Twiggs" and the Adelphians in the Adam and Eve sequence of "The Apple Tree" April 1 will bring the Reston Players in "The Fantasticks," Act I; the Phoenix of Springfield, in a scene from "The Sunshine Boys" and Cedar Lane Stage in Megan Terry's "The Ex-Miss Copper on a Set of Pills." Details at 673-7709.

Gig Young will costar with Bibi Anderson and John Cullum in Arthur Miller's "The Archbishop's Ceiling," opening April 30 at the Eisenhower . . . India's noted dancer, Yamini Krishnamurti, an exponent of Bharatanatyam, will perform tonight at 8 in the Department of Commerce auditorium . . . Harvard's Hasty Pudding theatricals will present its 129th annual original, "Cardinal Knowledge" Sunday night, April 3, in Lisner Auditorium; tickets now at the Washington Performing Arts Society, 1300 G St. NW.