WASHINGTON (AP) _ The Supreme Court, in a case involving a black man's murder by Ku Klux Klan members, today allowed criminal defendants to exclude potential jurors because of their race.

The court, over two dissenting votes, rejected arguments by Alabama prosecutors - supported by law enforcment officials nationwide - that defense lawyers unlawfully are seeking to impanel an all-white jury in the Klan case.

Justices Byron R. White and Anthony M. Kennedy voted to hear arguments in the case but four votes are needed to grant such review.

The issue was whether a 1986 Supreme Court ruling against racial discrimination in jury selection applies to defendants as well as prosecutors.

The court in 1986 ruled that prosecutors may not disqualify potential jurors based on their race. The 7-2 decision curtailed dramatically the traditionally broad power of prosecutors to strike prospective jurors from trials by using ''peremptory'' or automatic challenges.

The ruling, which overturned a black man's conviction by an all-white jury in Kentucky, established that the Constitution's equal-protection guarantees bar racially motivated jury selection by prosecutors.

But the decision left unanswered whether the same guarantees apply when defense lawyers seek to mold the racial make-up of the jury.

Generally, constitutional safeguards prohibit abuses by the government and not by private citizens.

The case acted on today stems from the March 21, 1981, killing of Michael Donald, 19, a black man who lived in Mobile, Ala.

Donald was abducted at random from a city street, beaten to death and his body hanged from a tree. Prosecutors said he was the victim of a Klan hunting party retaliating for a jury's inability to reach a verdict in the trial of a black man accused of murdering a white police officer.

Klan members Henry Francis Hays and James ''Tiger'' Knowles were charged in connection with the slaying.

Hays was convicted of murder and was sentenced to death. Knowles pleaded guilty to a federal charge of violating Donald's civil rights and was sentenced to life in prison.

Mobile County prosecutors then charged Hays' father, Bennie Jack Hays, and Benjamin Franklin Cox with aiding and abetting the murder. The elder Hays and Cox are former KKK members.

Bennie Hays collapsed in court last February, prompting a mistrial for both defendants.

An all-white jury already had been impaneled because of peremptory challenges used by the defense lawyers. The defense attorneys had disqualified all 16 blacks among 65 prospective jurors.

The elder Hays and Cox face retrial. In the interim, prosecutors appealed to the Supreme Court to test whether blacks may be excluded in a similar fashion once again.

Mobile County Circuit Judge Michael E. Zoghby ruled last May, ''Under the law as it now exists, defendants do not have to give a reason for the exercise of their peremptory challenges.''

The Alabama Supreme Court refused to disturb the judge's decision.

State prosecutors argued that excluding jurors based on race fosters racial prejudice and ''harms all members of the minority excluded from jury service'' by suggesting they are inferior.

The prosecutors said the most recent nationwide statistics show that in 1986 there were 81,000 cases - not including murders and kidnappings - in which blacks were victims of violent crimes committed by whites.

Allowing blacks to be barred automatically from juries in such cases is unlawful discrimination, the prosecutors said.

Defense lawyers for Hays and Cox said barring blacks helps assure the defendants a fair trial. One attorney said he also would move to disqualify ''Jewish people if I had a PLO (Palestine Liberation Organization) defendant.''

The appeal by Alabama prosecutors was supported by the National District Attorneys Association, attorneys general from nearly every state, the Southern Christian Leadership Conference and the Southern Poverty Law Center.

The case is Alabama vs. Cox, 88-630.