Lon A. Lewis, whose conviction in a 1977 "You kill my wife, I'll kill yours" murder plot was reversed by the Maryland Court of Appeals in August, yesterday pleaded guilty to one count each of first-degree murder and second-degree murder in the same case.

Following the plea, which was the result of plea bargaining between prosecutors and Lewis' attorney, the 29-year-old Bowie man was sentenced to life imprisonment on the first-degree murder charge.

However, Circuit Court Judge Jacob S. Levin said that after Lewis had served 50 years, the remainder of his sentence would be suspended. Levin also sentenced Lewis to 30 years' imprisonment on the second-degree murder charge, and ordered that the two sentences be served concurrently.

According to Lewis' attorney, Fred Warren Bennett, Lewis will be eligible for parole after 10 years. He would have been eligible for parole after 18 years under his sentence in the earlier case.

The conviction of Gene T. Meyer, 30, the man who agreed to the plot with Lewis and who then stabbed Lewis's 28-year-old wife and 4-year-old daughter to death in their Bowie home, recently was upheld by the Court of Appeals.

At his own trial last year, Lewis testified that Meyer first suggested the murders when the two men were in San Antonio, Tex., receiving advanced training as computer technicians.

According to Lewis's testimony, Meyer offered to kill Carol Lewis so that Lewis would be able to continue his relationship with his girlfriend.

Six months later, Meyer went into the kitchen of the Lewis home, picked up a butcher knife and killed Carol and Heather Lewis. Two weeks after the murder, under questioning by county police, Lewis confessed to his role in the plot.

Meyer was arrested the following morning. Subsequently he, too, confessed.

The plot also called for Lewis to kill Meyer's wife, Hortensia, so Meyer could collected a $100,000 insurance policy, Lewis testified last year. However, Lewis said, he thought the plot was "all a game" and never attempted to kill Hortensia Meyer.

The Court of Appeals had reversed Lewis's conviction because of a technical error made by prosecutors, At the time, Lewis was serving a sentence of life plus 30 years at the state prison at Hagerstown.