Mr. Donald's sister and brother, who sat through the trial and sentencing, left the courtroom without commenting.

But Mr. Hays's father, Bennie Jack Hays, a 67-year-old leader of the United Klans of America, said his son was not guilty and denounced the proceedings as the work of ''liars and Communists.''

''I'm the one they're picking on,'' the elder Mr. Hays added. ''To get to me, they got my son.''

The younger Mr. Hays was convicted largely on the testimony of James Knowles, another Klansman, who pleaded guilty to a Federal charge of violating Mr. Donald's civil rights. He is awaiting sentencing. The Federal charge carries a maximum penalty of life in prison.

Mr. Knowles testified that Mr. Donald was snatched off a Mobile street at random and killed ''to show Klan strength in Alabama.'' The Federal Bureau of Investigation contended that the killing was a Klan plot in retaliation for the mistrial of a black man accused of killing a white police officer. High Court Decision Cited

Mr. Donald, who had gone out that night to buy cigarettes, was beaten and strangled with a rope in a neighboring county. His body was brought back to Mobile and hanged from a scraggly tree across the street from his apartment.

Mr. Galanos called the case a ''sordid, sickening saga,'' and argued that a Supreme Court decision in a Florida case upheld the death sentence because the crime was one of racial hatred. In that case, he said, blacks killed a white person.

M. A. Marsal, a defense attorney who is seeking a new trial for his client, had sought to delay the sentencing on the ground that a ''surprise witness'' said another person killed Mr. Donald.

The police went to a Mobile County residence and a motel in search of the woman who was said to have called Mr. Marsal, but were unable to find her.