The Supreme Court ruled unanimously yesterday that a lawyer did not violate his client's constitutional right to effective counsel when he thwarted the client's plan to lie on the witness stand.

"The right to counsel includes no right to have a lawyer who will cooperate with planned perjury," Chief Justice Warren E. Burger wrote in an opinion joined by four other justices.

A lawyer's duty to a client, he said, "is limited to legitimate, lawful conduct compatible with the very nature of a trial as a search for truth. Although counsel must take all reasonable lawful means to attain the objectives of the client, counsel is precluded from taking steps or in any way assisting the client in presenting false evidence or otherwise violating the law."

In a concurring opinion, Justice Harry A. Blackmun said he was "troubled by the court's implicit adoption of a set of standards of professional responsibility in state criminal proceedings" and warned that "except in the rarest of cases, attorneys who adopt 'the role of the judge or jury to determine the facts' pose a danger of depriving their clients of the zealous and loyal advocacy required by the Sixth Amendment." But Blackmun, joined by Justices William J. Brennan Jr., Thurgood Marshall and John Paul Stevens, agreed that the lawyer's actions did not prejudice the defendant's constitutional rights.

The case, Nix v. Whiteside, involved an Iowa man, Emmanuel Charles Whiteside, who said he stabbed a man to death in self-defense. Whiteside, who had said consistently he had not seen a gun during the drug-related killing, changed his story less than a week before trial, telling his lawyer, Gary L. Robinson, that he had seen something "metallic" in the victim's hand just before stabbing him.

Robinson threatened to withdraw from the case and tell the judge that Whiteside was lying. Whiteside backed off the plan, testified and was convicted of second-degree murder. The 8th U.S. Circuit Court of Appeals granted him a new trial, ruling that Robinson "went so far in his . . . zeal to avoid deceiving the court that he became an adversary to his own client."

In overturning that decision, Burger said Whiteside's perjury plan was "indistinguishable in substance" from a scheme to threaten or bribe a witness or juror. "An attorney's duty of confidentiality, which totally covers the client's admission of guilt, does not extend to a client's announced plans to engage in future criminal conduct," Burger said.

Brennan, in a separate concurring opinion, termed Burger's "essay" on the "thorny" issue of what a lawyer should do when a client plans to commit perjury "pure discourse without force of law."