LOS ANGELES, July 1 (AP) --- Tim Buckley, the rock star, died, apparently of a heart attack, on Sunday at the age of 28.

A spokesman for the singer said Mr. Buckley died while climbing a flight of stairs at his Santa Monica apartment. An autopsy has been scheduled.

Mr. Buckley was noted for his recordings of his own compositions of "Sweet Surrender," "Pleasant Street" and "Move With Us."

He rose to popularity as a teen-ager and was signed by Electra Records to write and record his own songs and ballads. As he grew older, his work became more experimental and his popularity declined, a recording source said.