Five singers, each one hoping to win the big $65,000 first prize next Saturday night, sang their heads off and their hearts out yesterday in the Terrace Theater of the Kennedy Center. They are the first five semifinalists in the song competition -- sponsored by the Center and the Rockefeller Foundation -- for excellence in the performance of American music. The other five will sing today. On Saturday, three finalists chosen from the 10 will sing for an hour each in the Concert Hall, starting at 6 p.m.

Critical opinions of yesterday's singing are inappropriate because the judges have yet to hear all 10. But it can be said that all of these singers are obviously proficient, though some are more so than others. Since the purpose of the competition is to help restore the American art song -- and the art of song recitals -- to the public popularity they used to occupy, the winner or perhaps winners, of this contest will, as a part of the prize, enjoy a busy concert tour of song recitals.

Yesterday began with Barbara Hocher, a lyric soprano who won high praise for her singing in this summer's Terrace Therater production of "Postcard From Morocco."

She was followed by Charles Roe, a baritone who has taught voice at Texas Tech and Eastern Michigan University and will this fall join the faculty of the University of Southern California. He made his New York City opera debut five years ago as Nero in Monteverdi's "Coronation of Poppaea."

Mezzo Barbara Martin was next, the only singer in the semifinals to include an American popular song, Cole Porter's "I Get a Kick Out of You," among her offerings. She preceded it with George Crumb's extraordinary Third Book of Madrigals.

The youngest competitor, baritone Sanford Sylvan, who is 25, followed, and reminded some who were listening of last weekend's youthful success at the U.S. Open in tennis.

The last singer of the day was Metropolitan Opera tenor -- the only tenor in the final 10 -- James Atherton, who was much admired at Wolf Trap this summer as the Chaplain in "The Dialogues of the Carmelites" by Poulenc. He had the wit to chose his recital, which ended five hours of singing, with Purcell's "Music for a While."