The Maryland Court of Appeals yesterday ordered a new trial for confessed murderer Lon A. Lewis after reversing his conviction in a 1977 "You Kill My Wife, I'll Kill Yours" murder plot because of a technical error by the prosecution.

But while reversing the Lewis conviction, the appeals court noted that the technical rule on which the case was overturned was "unsound" and would be stricken from the state's legal regulations. That rule requires than an accessory to murder cannot be tried until after the sentencing of the principal in a murder.

Lewis was convicted as the accessory and Gene T. Meyer as the principal in the 1977 murder of Lewis's 28-year-old wife and four-month-old daughter at their Bowie home. The appeals court said Prince George's County prosecutors erred by bringing Lewis to trial 11 days before Meyer was sentenced.

Lewis is currently serving a life sentence at the state prison in Hagerstown. With the convictions reversed he is now being held on a bond of $50,000, meaning that if he can raise $5,000 for the bond fee he can go free while the new trial is pending.

His coconspirator, Meyer, also is serving a life sentence. His appeal is still pending. Meyer is serving his sentence in Baltimore. The two men have been kept apart since June 1978, when Meyer was indicated on charges of soliciting four murders while in jail, including Lewis's.

"There can be no doubt that [Lewis's] trial was improper," Judge John C. Eldridge wrote in the court's 23-page opinion.

Yesterday's ruling marked another chapter in a bizarre story which began unfolding in April 1977, Lewis, then 27, and Meyer, also 27, were both in San Antonio at a training school for Baltimore's Data Point Corp., where both worked as computer technicians.

While there, Lewis, who had separated from his wife temporarily during 1976 but later reconciled with her, met Cathy Nugent, then 18 and, according to his written confession, had an affair with her.

Over dinner in San Antonio, Lewis testified, Meyer suggested that if Lewis wanted to be free of his wife to be with Nugent, Meyer could, "take care of things back home if you want."

"You mean kill my wife" Lewis said he asked.

"Right," Meyer answered.

That conversation hatched a plot which culminated six months later when Meyer went to Lewis's home at 4807 Raemore Drive, Bowie, and slashed Carol and Heather Lewis to death with a butcher knife.

Lewis, who had been told by Meyer the previous night to work late, arrived home 30 minutes after the murders and found the bodies. Police said they were found in "gallons of blood," and John Rhoads, the former Prince George's County police chief, described the scene as "the worst I ever saw in 22 years as a cop." month into evidence. detectives, who had found letters written to Cathy Nugent and incriminating poems in Lewis's desk, Lewis confessed to the plot. Meyer was arrested the following morning and also confessed.

After Carol Lewis was killed, the conspiracy plan called for Lewis to kill Hortensia Meyer, Meyer's wife, so Meyer could collect on a $100,000 insurance policy.

At Lewis's trial, his attorney, Leslie L. Gladstone, argued that Lewis could not be found guilty of murder as an accessory before the fact because the prosecution had not introduced Meyer's conviction the previous month month into evidence.

"Why couldn't you have done that?" Judge Jacob S. Levin asked prosecutor Joseph C. Sauerwein.

"Because, your honor, Meyer hasn't been sentenced yet and his conviction is not a matter of record until he's sentenced."

In the ruling yesterday, the appeals court found that because Meyer's conviction was therefore not final, Lewis could not be tried under the procedural rules then in effect.

Gladstone also argued at the trial that Lewis's confession should not be admitted into evidence because it was not "voluntary." Lewis testified that he was told by a detective that failing to take a lie detector test amounted to an admission of guilt and said that he asked on several occasions to speak to an attorney and was told, "only murderers need lawyers." The police denied these claims.

The court did not rule on whether Lewis's confession was voluntary but said did say, "although concluding that the defendant's confession was voluntary, the trial court failed to resolved, the factural disputes . . . on remand, if the same discrepanices in the testimony arise, the trial court sbhould resolve them and clearly set forth its findings."

"Particularly troublesom," the court continued, " are the allegations of the police misstatements concerning requests for an attorney."

Finally, the court found that Lewis could not be convicted of both murders as an accessory before the fact and solicitation of murder as he was at the trial. He can be convicted of only one of the two, the court found.

Reacting to the reversal yesterday, Gladstone said: "Well, I'll be a Sonuvabitch. I argued that point until I was blue in the face at the trial.

"If Lon Lewis were to go free I think justice would be served because no matter what happens he'll never be the same. I know that very few people agree with that but that's the way I feel."

Gladstone said he had talked to Lewis's parents who were "delighted but in shock," about the reversal and "planned to contact Lewis in the next few days about the new trial."

Prosecutor Sauerwein was out of town and could not reached for comment. A spokesman for the state's attorney's office said that no one in the office would comment with a new trial pending.

Tom Saunders, one of two appelate attorneys who presented the appeal on the part of Lewis, said he believed it was the prosecution's error which caused the reversal.

"They should have been aware of the state rules of procedure," Saunders said. "They should have known that trying an accessory before a principal is sentenced wasn't allowable under the rules. Yes, they did make a mistake."

Ray Davis, the assistant attorney general who argued the appeals case for the state disagreed, saying "It wasn't really the prosecutor's error. In order to see how the common law applied, I had to go back and study law books and cases from the 1800s. I'm not sure that most criminal attorneys knew that rule applied.

Davis also said he was delighted that the court had thrown out the rule for future cases. "We conceived of a myriad of circumstance under which the principal could not be tried, therefore making it impossible to try the accessory," he said. "For instance, if the principal in a murder flees to the another continent, but his accessory is caught."

Lewis testified during his trial that as the plot unfolded he had thought "it was all a game." He said then and during an interview in prison that he had no explanation for his actions.

At his sentencing, when Sauerwein commented that he wished Lewis could face the death penalty, Lewis told Levin, "I do deserve the death penalty. It would make me the happiest guy in the world."