The Virginia Supreme Court yesterday upheld death sentences imposed on three convicted murderers, including a man found guilty in a Fairfax County murder-for-hire scheme.

James T. Clark Jr., 22, was sentenced to death last year for the hired killing of George Harold Scarborough, a Fairfax gas station operator, who was shot in January 1978 as he entered his Franconia home.

The other men whose death sentences were affirmed by the state Supreme Court yesterday were Charles Sylvester Stamper, convicted in a triple slaying at a Richmond area restaurant, and Frank Coppola, found guilty of killing a Newport News woman during a robbery of her home.

Lawyers for all three men said yesterday that they planned to appeal the Supreme Court rulings. The men are among seven convicted murderers currently imprisoned at the maximum-security Mecklenburg Correctional Center and sentenced to die in the state's electric chair.

The electric chair, located at the State Penitentiary at Richmond, has not been used since 1962. No once is expexted to be executed in Virginia for some time because of continuing court appeals of the prisoners' death sentences. Virginia's death penalty law was revised in 1977 by the General Assembly to comply with U.S. Supreme Court rulings on capital punishment.

In upholding Clark's death sentence, the Supreme Court rejected all of his lawyers' arguments. A key contention by Clark's attorneys was that the death penalty was disproportionately severe because another man convicted in the murder-for-hire plot, Charles D. Stewart, was sentenced to life imprisonment.

Clark and Stewart were alleged by the prosecutors to have been hired to murder Scarborough at the request of the victim's estranged wife, Jamie. She was acquitted last year, however, of charges that she had hired the two men through an intermediary to kill her husband.

Fairfax prosecutor Robert F. Horan Jr. had recommended life imprisonment for Stewart, a cousin of Clark, partly because Stewart assisted prosecutors by testifying in a related trial. In addition, prosecutors alleged that Clark had fired the shots that killed Scarborough.

The state Supreme Court held that Horan's recommendation of a lesser penalty for Stewart could not be construed as an 'unconstitutional or improper exercise of discretion."