Spoken words have found their place next to museum artifacts at the Smithsonian Institution, where the Pittsburgh-based International Poetry Forum will present Washington with its third season of poetry and music showcases. "Word/Song III," the series of six Sunday evening programs continuing through March 1985, begins at 7:30 tonight with the appearance of Caribbean poet Derek Walcott and musician Nathan Davis with the ensemble Tomorrow in the auditorium of the Hirshhorn Museum and Sculpture Garden.

"They are original programs," says Anne Mullin Burnham, the Forum's Washington liaison. "The great strength of it is that you are hearing poetry that comes from so many cultures . . ." Walcott, an honorary member of the American Academy and Institute of Arts and Letters, is described by Forum director and founder Samuel Hazo as "one of the best poets I've read in the last 30 years." Hazo, a poet and professor of English at Duquesne University in Pittsburgh, selects the materials for the performances.

Since its beginnings in Pittsburgh in 1966, the Forum has brought over 600 actors and poets, including Archibald MacLeish, Jorge Luis Borges, Claire Bloom, Dame Judith Anderson and the late Princess Grace of Monaco, before audiences. Its Washington "road shows" are the same programs it continues to present to capacity audiences at the 600-seat Carnegie Lecture Hall in Pittsburgh.

The move from the Wolf Trap Barns, where the 18-year-old Forum first staged the programs two years ago, is intended to attract Washingtonians who may have found that Virginia locale "somewhat remote," says Hazo. Janet Solinger, director of the Smithsonian Resident Associate Program, which is presenting the programs with the Forum, believes that the Institution is ready to accept poetry as "museum-quality knowledge."

Hazo hopes the Forum will continue its stay with the Hirshhorn. "Ultimately," he says, "poetry is an aural art and an aural art needs someone to listen. We've added another color to their Smithsonian's magnificent spectrum of offering. There's a little touch of what has been almost a habit in the city of Pittsburgh since 1966 now in Washington."

For tickets and information, call 357-3030.