While 20 of the 29 shows in the First New York International Festival of the Arts theater section are new or contemporary works, some of this century's most influential playwrights do get a doff of the hat. In a few cases, they get a bit more.
Rotating performances of ''Long Day's Journey Into Night'' and that dark play's halcyon mirror image, ''Ah, Wilderness!'', offer a short course marathon on Eugene O'Neill, for example. And Samuel Beckett recommended the Gate Theater of Ireland's production of ''Juno and the Paycock'' to the festival; that company will make its American debut with the Sean O'Casey play and then return Mr. Beckett's compliment with a second show, ''I'll Go On,'' based on the Beckett novels ''Molloy,'' ''Malone Dies'' and ''The Unnameable.''
A visiting Soviet troupe will offer a marathon of its own: the Maly Drama Theater of Leningrad, in its American debut, will present ''Brothers and Sisters,'' a seven-hour, two-evening work about life in a Soviet village during and after World War II. Notable among the other imported, large-scale productions will be the Haifa Municipal Theater's staging of ''Ghetto,'' Joshua Sobol's explosive drama about a Jewish theater company struggling to survive in the Vilna ghetto.
A fair sample of contemporary avant-garde work will be available, with many artists familiar to adventurous theatergoers. They include Tadeusz Kantor and his Cricot 2 company from Poland and ''Miracolo D'Amore,'' Martha Clarke's latest amalgam of music, dance and theater, which is scheduled to open here after an initial presentation in Charleston at the Spoleto Festival. Realism and the Musical
Though the festival is devoted to the performing arts of the 20th century, American realism and the Broadway musical are among several important movements thinly represented; there is only a single native offering from the first half of the century (''Ah, Wilderness!''). But good use is made of the many small companies that produce in the city year-round. The Off Broadway series ranges from evenings of new one-acts to full-scale new plays such as ''El Senor Presidente,'' a work developed for the annual Festival Latino by a Latin American ensemble under the direction of Carlos Gimenez.
Special programs include a look at Joan of Arc by female directors from around the world (part of the Women's Project's ''Mapping Theatrical Territories'') and an international program of childrens' theater.
The festival will take place from June 11 to July 11, in New York City. Tickets will be available from the festival ticket service beginning Feb. 14, or directly from the individual box offices. Calendars and ticket order forms can be obtained by writing to the New York International Festival of the Arts, 127 East 73d Street, New York, N.Y. 10021.
The Programs 
''AVVAKUM.'' Gardzienice company of Poland. Cathedral of St. John the Divine, June 14-18, 21-25. 

''MIRACOLO D'AMORE.'' Martha Clarke company. Public Theater, June 14-19, 21-26, 28-30, July 1-3, 5-10. 

''GHETTO.'' The Haifa Municipal Theater. Theater to be determined, June 14-19, 21-26, 28-30, July 1-3, 5-10. 

''I SHALL NEVER RETURN.'' Tadeusz Kantor's Cricot 2 company, from Poland. La Mama Annex, June 14-19, 21-26.

 ''JUNO AND THE PAYCOCK.'' by Sean O'Casey. The Gate Theater of Ireland. Theater to be determined. June 14-18, 20-25, 27-30, July 1-2.

 ''LONG DAY'S JOURNEY INTO NIGHT'' and ''AH, WILDERNESS!'' Performed in repertory. Theater to be determined, June 14-19, 21-26, 28, 29, July 1-3, 5-10. 

''THE NIGHT OF THE IGUANA.'' Circle in the Square Theater (Uptown). June 14-19, 21-26, 28-30, July 1-3, 5-10. 


OFF BROADWAY TRIBUTE TO THE AMERICAN PLAYWRIGHT. 
''V & V Only,'' Sheridan Square Playhouse, June 14-19, 21-26. 28-30, July 1-3, 5-10. 

One-Act Marathon, Ensemble Studio Theater. June 15-20, 22-27, 29, 30, July 1-4, 6-10.

''Alma,'' ''Welcome back to Salamanca,'' Intar Theater, June 15-19, 22-26, 29, 30, July 1-3, 6-10. 

''Flow My Tears, the Policeman Said,'' Mabou Mines at New York University, Tisch School of the Arts, June 17-19, 21-26, 28-30, July 1-5, 7-11. 

''A Circle,'' Theater for the New City, June 20, 22-27, 29, 30, July 1-3, 6-10. 

'Boutique Living and Disposable Icons,'' Pan Asian Repertory Theater at the Perry Street Theater. June 21-26, 28-30, July 1-3, 5-10. 

''Jika,'' New Federal Theater at the Henry Street Settlement Playhouse, June 30, July 1-3, 7-10. 

PAVLOVSKY MARATHON. Stages Theater of Los Angeles at the Clurman Theater, June 15-20, 22, 23, 24-27. 

''BROTHERS AND SISTERS.'' Maly Drama Theater of Leningrad. Belasco Theater, June 16-18, 20-25, 27-30, July 1, 2. 

CHILDRENS FARE. Yinchuan Beijing Opera Troupe, Theatre de l'Ombrelle, La Troupe Circus, Fred Penner, Bob McGrath, Jackie Torrence, Masaji Terasawa, at the Triplex Theater, June 16-19. 

''SAND.'' Mosaic Theater at the 92d St. Y, June 16, 18, 19, 21-23, 25, 26, 28-30, July 2, 3, 5-7, 9, 10. 

''EL SENOR PRESIDENTE''. Public Theater, June 17-19, 21-26, 28-30, July 1-3, 5-10. 

''EXIT THE KING.'' The Acting Company, American Place Theater, June 19-26, 28-30, July 5-8. 

''STAND-UP COMEDY: A TWENTIETH CENTURY ART.'' Robert Klein, Circle in the Square (Uptown). June 19, 20. 

''WATER STATION.'' Tenkei Gekijo company from Japan. Japan Society, June 19-22.

''THE RITUAL OF SOLOMON'S CHILDREN.'' Teater Rendra, from Indonesia, St. Ann's Center for Restoration and the Arts, June 21-26. 

''YOU HAVE COME BACK.'' Ubu Repertory, St. Clement's Church, June 21-25, 28-30, July 1, 2.

 ''I'LL GO ON.'' The Irish actor Barry McGovern; theater to be determined. June 24-26, 28-30.

 MAPPING THEATRICAL TERRITORIES. The Women's Project and Productions, Apple Corps Theater, June 24-26, 28-30, July 1-3.