A judge Monday rejected a bid to reopen the trial of the Sharpeville Six, and the blacks convicted for a mob murder once again face hanging unless President P.W. Botha intervenes.

But the president has already turned down an appeal for clemency. In doing so, he spurned an international campaign to spare the six, who were found guilty in the mob killing of a black town councilor.Pretoria Supreme Court Justice Willem Human, who presided over the original trial in 1985, turned down an application by defense lawyers to reopen the case to review allegations that police coerced two state witnesses.

The defendants - five men and a woman - were convicted of complicity in the 1984 death of Khuzwayo Dlamini, who was stoned to death and burned during riots provoked by a rent increase.

Human said despite allegations of coercion involving the witnesses, there was ample uncontested evidence to implicate all six defendants. He described the defense request as "frivolous and absurd."

He said the only remaining hope for saving the six lay in petitioning Botha again. Relatives and diplomats crowded the courtroom during the reading of the decision, but there was little reaction.

Defense attorney Prakesh Diar said he would try to win an extension of the stay of execution and attempt to petition the chief justice to reopen the trial. But he said the fate of the six was really in Botha's hands.

"I hope and I pray that the state president will reconsider his previous decision. This is a politically related case. (Botha's decision) may be based on political considerations."