A federal judge has overturned the sentence of Virginia death row inmate James T. Clark Jr. in a 1978 murder-for-hire case in Fairfax County and ordered he be resentenced, declaring that Clark was not effectively represented when he was condemned to die.

The decision, by U.S. District Judge Albert V. Bryan Jr. in Alexandria, said defense lawyers failed to portray details about Clark's upbringing that might have evoked sympathy in the jury that recommended in 1978 that he die in the state's electric chair.

Among those details, Bryan said, were the fact that Clark's mother was a prostitute, that his parents were separated, that his brother had been murdered, that Clark had been burned over 40 percent of his body at age 10 and that he lived with another prostitute as an adolescent.

The judge said those factors, which were known to the defense, might have balanced the jury's impression of Clark during the sentencing phase of the trial as a man who committed the murder "for the money, the excitement and the thrill."

Fairfax County prosecutor Robert F. Horan Jr., who personally handled the Clark case, said yesterday he was stunned by Bryan's ruling and would ask that the Virginia attorney general appeal it. If that fails, Horan said he will argue at any new sentencing that Clark should be executed. "If anyone ever deserved the death penalty, James Clark did."

Bryan's ruling this week agreed with a controversial decision by Fairfax Circuit Judge Richard J. Jamborsky, who had sentenced Clark to death in 1978 but four years later reversed himself on grounds that Clark's lawyers had performed inadequately.

The state attorney general's office appealed Jamborsky's commutation of the death sentence and it was reinstated last June by the Virginia Supreme Court. Clark was scheduled to die Dec. 20 before filing his latest appeal.

Clark, 27, was one of three persons convicted in the Jan. 31, 1978, slaying of a Springfield service station owner, George Harold Scarborough. According to prosecution testimony, Clark and his cousin, Charles D. Stewart, both of Clinton, were hired by Scarborough's estranged wife, Jamie, to kill Scarborough.

Clark and Stewart attempted to smother Scarborough with a chloroform-soaked pillow at Scarborough's townhouse, then shot him, prosecutors charged.

Stewart and Betty M. Holler, a friend of Jamie Scarborough's who acted as an intermediary in the murder plot, both were sentenced to life in prison. Jamie Scarborough was acquitted of charges that she hired the killers.

In his opinion, Bryan noted that Clark appeared to favor his own execution. Shortly after his indictment, Bryan said, Clark told his attorney "he would agree to testify against others implicated in the alleged murder for hire in exchange for the death sentence with no recommendation for life." The judge said Clark's attorney "found this request bizarre to say the least."

Bryan wrote "that faced with almost certain defeat at the guilt stage of the proceeding, with the only hope for their client to be the presentation of some evidence at the sentencing phase, trial counsel's failure to seek out (mitigating) psychiatric evidence . . . was unreasonable.

"This failure," Bryan continued, "denied Clark reasonably effective assistance, and counsel's performance . . . fell below the range of competence demanded of lawyers in criminal cases."

Clark's two trial defense lawyers, Ian Rodway and Gary V. Davis, were unavailable for comment yesterday.