It is hard to think of any writer who more searchingly or richly captured the spirit and mood of this country in the 1930s than did John Steinbeck. Look at the books he turned out in those years: "TOrtilla Flat" in 1935; "Of Mice and Men" in 1937, in both its novel and dramatized form: "Red Pony" that same year, and two years later, "Grapes of Wrath."

These are more than enough to entitle Steinbeck to his high place among this country's literary giants. Remember, too, that "Cannery Row" was still to come in 1945 and "The Wayward Bus" two years after that. And in addition to these there were "East of Eden," "The Moon Is Down," and a dozen more.

No one surpassed Steinbeck in capturing the terrible frustration of the migrants and their defiant despair as they hit California during the Depression . . . the migrants who piled what they could into their autos or trucks and headed for any place that looked green, hoping they could settle there.The migrant workers were his richest lode because he know their problems, their language, their buried hopes and their still-struggling ambitions.

Each Steinbeck enthusiast has his favorite, though some of them will admit that they cannot narrow the choice down to one. It is too hard to give up one of those unforgettable portaits of plain men and women caught up in the bitter drought of the Mice and Men" and "Grapes of Wrath" put into our fiction what Pare Lorentz and Virgil Thomson wrote on film and in music.

When Aaron Copland composed the music for the film "Red Pony," he turned with his amazing ease to cowboy songs with which to enrich his score. When Thomson wrote the music for the sere scenes in Lorentz' documentary, "The Plow That Broke the Plains," he mixed, with brilliant cunning, his own ideas with folk and work songs of the devastated Midwest he was setting to music.

Carlisle Floyd turned to Steinbeck's "Of Mice and Men" in the late 1960s. Fifteen years before he had scored a lasting public hit with his music drama, "Susannah." No one else has put into music the flavor of that Kentucky hill country drama, adapted from an Old Testament story, that Floyd did in the work that gave him lasting public favor. (Floyd avoids the label "opera" in describing his works for the musical stage.) A few years later his version of "Wuthering Heights" was met with wildy mixed reactions. It has not proved a success.

In January 1970, when the Seattle Opera gave the premiere of Floyd's setting of the Steinbeck novel, drawing also upon its stage version, Floyd scored a triumph both with audiences and critics. The reasons are not hard to discover. Steinbeck's drama is simple and homey. And in its inevitable movement toward a final tragedy, it has that fatal power to make us wish that the end we know is coming might somehow be avoided.

From the beginning we feel strong sympathy for Lennie, the migrant worker who has the physique and strength of a giant and a child's mind." We want things to work out so that Lennie and his friend, George, will be able to buy a house and farm of their own. But we know that Lennie has killed a mouse he found, that he will kill a puppy of which he was fond. We know that he loves soft things. He sings, "It was somethin' I could stroke, somethin' I could pet and it belonged to me. It was somethin' small, not growed up yet, somethin' soft with fur and I could stroke an' pet it like I love to do."

Knowing this, how can we help worrying when Curley's wife stops in the barn to visit with Lennie as she is getting ready to run away from the ranch. She is pretty and she has such soft hair. She even invites Lennie to feel it . . . and so the final tragedy strikes.

The Kennedy Center, having seen the success of former Houston Opera productions, is bringing in the Houston staging of "Of Mice and Men" to the Opera House for three weeks, beginning Tuesday. In recent seasons, Houston has sent Washington and New York outstanding productions of "Treemonisha," "El Capitan" and "Porgy and Bess."

"Of Mice and Men" will be staged by Frank Corsaro, whom Floyd remembered in a special note when his score was published:

"The composer wishes to acknowledge gratefully the special contribution of Frank Corsaro, many of whose imaginative ideas for the staging of this musical drama have been incorporated into the present edition.

The Kennedy Center decided to give "Of Mice and Men" a three-week run in the oper House because, according to the Center's Roger L. Stevens, "We import a lot of foreign opera to this country and we are always giving operas from other countries. I just think we ought to do more for American opera.

"We ran 'Of Mice and Men' here as a play last year and sold out," he said."I think that Carlisle Floyd's opera works better even than the play. So I thought we ought to do it. I think the public will enjoy it."

The cast at the Kennedy Center will be headed by Robert Moulson, the Lennie of the original Seattle performances. The opera will be given Tuesday through Saturday evenings, with matinees on Saturday and Sunday.