Singers, orchestras, string quartets, and even a prize-winning Trinidad steel band will be included among the attractions of the Inter-American Music Festival. There is free admission to all the concerts.

The 25th annual festival runs from this weekend through May 17 at the Kennedy Center, the Organization of American States and the National Academy of Sciences.

The emphasis in this festival is on modern music, chiefly because most of the serious music of North and South America dates from the 20th century. This year's attractions will include American and Canadian ensembles performing music by composers from Brazil, Mexico, Colombia, Argentina, Cuba, Panama and Venezuela as well as works from the U.S. and Canada.

Among the performing groups will be the Los Angeles Contemporary Music Ensemble, the Manhattan Vocal Ensemble, the Galliard Music Ensemble from Canada, and the West Indian Tobacco Co. Desperadoes Steel Band, winners of this year's Carnival Steel Band Competition in Trinidad.

Ensembles from the Washington area will include an orchestra specially recruited for the festival, the Paul Hill Chorale, the Contemporary Music Forum, the Peabody Symphony Orchestra, the New World Chamber Players, and the Manchester String Quartet, made up of members of the National Symphony Orchestra. THE CONCERTS FRIDAY, APRIL 29 -- 8:30, Kennedy Center Concert Hall. Festival Orchestra and Paul Hill Chorale; Jorge Mester, conductor; Luis Ascot, piano: Music of William Bergsma, Alberto Ginastera and Peter Mennin; world premiere of "Padre Liberator" for chorus and orchestra by Isabel Aretz of Venezuela. SATURDAY, APRIL 30 -- 8, OAS Hall of the Americas. Manhattan Vocal Ensemble, Nelly Vuksic, conductor; Cesar Vuksic, piano; music by Luis Antonio Escobar of Colombia. SUNDAY, MAY 1 -- 3, Kennedy Center Concert Hall. West Indian Tobacco Co. Desperadoes Steel Band; T & T Repertory Dance Co.; Calypso, folk and classical favorites. TUESDAY, MAY 3 -- 8, OAS. Contemporary Music Forum. Music of Alvin Etler, Gerardo Gandini, Marlos Nobre, Brian Bennett, Aurelio de la Vega; world premiere of "Romancero" by Mario Davidowsky of Argentina. SUNDAY, MAY 8 -- 4, OAS. Manchester String Quartet. Music of Harry Somers, Roque Cordero, Alberto Ginastera. MONDAY, MAY 9 -- 8:30, Kennedy Center Concert Hall. Peabody Symphony Orchestra, Peter Eros, conductor; Caio Pagano, piano. Music of Gundaris Pone, Jose Almeida Prado, Manuel Enriquez and Morton Gould. TUESDAY, MAY 10 -- 8, OAS. Galliard Music Ensemble. Music of Marjan Mozetich, Irving Fine, Heitor Villa-Lobos and Andre Prevost. WEDNESDAY, MAY 11 -- 8, OAS. Los Angeles Contemporary Music Ensemble. Music of Camargo Guarnieri, Alberto Ginastera, Henri Lazarof and Robert Linn. TUESDAY, MAY 17 -- 8, National Academy of Sciences. New World Chamber Players. Music of Silvestre Revueltas, Jorge Antunas, Leslie Bassett and Alberto Ginastera.