BIRMINGHAM, Ala. (AP) _ The U.S. Supreme Court on Thursday refused to block the deportation of five Cubans held in Alabama, clearing the way for the first repatriation of Mariel boat people since a 1987 agreement with Cuba.

The detainees are scheduled to leave for Cuba from the Birmingham airport Friday morning. Announcement of the repatriation agreement sparked uprisings last year at two federal prisons where the Cubans were held.

Two of the five detainees did not oppose deportation, and the other three lost their legal fight when Supreme Court Justice Anthony M. Kennedy, without comment, denied their emergency application for a stay of repatriation.

The three previously were turned down by a federal judge in Birmingham and by the 11th U.S. Circuit Court of Appeals in Atlanta.

The government had planned to fly the five to Cuba on Thursday, but postponed the flight after Cuba asked for more time to prepare for their arrival.

The five left Cuba in the 1980 boatlift from Mariel, Cuba, but were placed in custody in America pending deportation because of their criminal records in this country. They have been imprisoned at Talladega, 60 miles east of Birmingham.

Some of the 125,000 people in the illegal boatlift were convicts or mentally ill.

The Justice Department said deportation of the five would resume a repatriation program that began in 1984. The five are among 15 Talladega inmates designated for return to Cuba after reviews by panels the Justice Department set up a year ago.

U.S. District Judge U.W. Clemon said he will decide by Monday whether to delay the return of the other 10.

The United States is trying to return to Cuba as many as 2,500 Marielitos as ''excludable aliens,'' or those convicted of serious crimes in this country. Attorneys for the inmates argue they will be persecuted if they are sent home.

The government sent back 201 Cubans several years ago, but Cuban President Fidel Castro halted the repatriations in 1985 before agreeing last year to accept 2,746.

That agreement resulted in riots by Cubans in federal prisons at Atlanta and Oakdale, La. The detainees later were dispersed, and 114 are at Talladega.

In asking Clemon not to order a delay, attorneys for the Immigration and Naturalization Service said the 13 had received full reviews of their cases. The attorneys accused the Cubans of using delaying tactics.

The three who sought court intervention are Miguel Beitia-Socarraz, 28, who pleaded guilty to second-degree burglary; Onel Calzado-Garlobo, 43, convicted in 1982 of attempted sexual assault charges involving a 13-year-old girl; and Rene Maurin-Oliva, 25, who pleaded guilty to theft and battery.