By a single vote, the Supreme Court yesterday upheld the death penalty of a man convicted of murdering a Virginia state trooper, rejecting claims that the jury mistakenly thought it could not impose life imprisonment instead. Dissenting justices protested that there was "a virtual certainty" the jurors didn't understand their instructions and that many wanted to spare the man's life.

Yesterday's decision, written by Chief Justice William H. Rehnquist and dividing the court along familiar ideological lines, clears the way for the execution of Lonnie Weeks Jr. He was within two hours of being put to death on Sept. 1 when the high court said it would hear his case. David Botkins, spokesman for Virginia Attorney General Mark L. Earley, said yesterday that an execution could take place as early as next month.

More nationally significant, the court's decision suggests that trial judges have minimal obligations to clarify instructions for jurors who are confounded by the legal language in a tough capital case.

"The problem is that jurors get so little guidance. To say judges have no requirement to assist them will simply lead to greater misunderstandings, particularly in death penalty cases," said College of William and Mary law professor Paul Marcus.

A separate dispute, involving indigent representation, produced the same 5-4 vote and another impassioned dissent about defendants' rights. The majority upheld a procedure that allows court-appointed lawyers to avoid filing client appeals that they deem frivolous.

The case tested the constitutional guarantee of effective assistance of counsel and a 1967 decision requiring a court-appointed lawyer who believes his client's appeal lacks merit to nonetheless file a brief identifying potential issues that might support an appeal.

Yesterday's decision in Smith v. Robbins upheld a California procedure--with parallels in several other states--that permits the lawyer to bypass legal arguments and instead simply describe the facts and procedural history of the case.

Joining Rehnquist in the majority on both decisions were Justices Sandra Day O'Connor, Antonin Scalia, Anthony M. Kennedy and Clarence Thomas. In dissent were Justices John Paul Stevens, David H. Souter, Ruth Bader Ginsburg and Stephen G. Breyer.

In the seven-year-old Virginia case, Weeks had been found guilty of firing six bullets at trooper Jose Cavazos during a traffic stop on Interstate 95 near Dale City, killing him on the spot. Weeks maintained that jurors never fully considered his background, character and feelings of remorse, violating the Eighth Amendment guarantee that jurors review all relevant mitigating evidence.

The record shows that the jurors were indeed in some sort of quandary. Prosecutors had argued that death was warranted based on two aggravating circumstances: that Weeks was a continuing danger to society and that his conduct was "outrageously or wantonly vile, horrible or inhuman."

During deliberations, the jurors asked the judge whether, if they believed Weeks guilty of at least one of those aggravating circumstances, it was their duty to give him the death penalty. The judge declined to tell them outright that they could still choose life imprisonment but instead referred the jurors to a written instruction, upheld in an earlier high court ruling. The instruction provided that if jurors found an aggravating factor present, they "may fix the punishment . . . at death, or if you believe from all the evidence that the death penalty is not justified, then you shall fix the punishment . . . at [life] imprisonment."

The jurors returned a verdict of death, and Weeks claimed the ambiguous instructions led them to believe that was their only option. He noted that as the jurors were polled about their decision, a majority were in tears.

The dissenting justices agreed: "Tragically, there is a reasonable likelihood that they acted on the basis of a misunderstanding of [their] duty," Stevens wrote.

But the Rehnquist majority in Weeks v. Angelone said it would presume the jurors understood the judge. "Given that [Weeks's] jury was adequately instructed and given that the trial judge responded to the jury's question by directing its attention to the precise paragraph of the . . . instruction . . . the question becomes whether the Constitution requires anything more."

Said Rehnquist: "We hold that it does not."