A 26-year-old Southern Maryland man was convicted today of kidnaping, rape and premeditated murder in the slaying of Stephanie Ann Roper, a Frostburg State College honor student he had offered to help after her car became disabled on a lonely road in rural Prince George's County.

Jack Ronald Jones could be sentenced to die in Maryland's gas chamber, but he displayed no emotion when the jury delivered its verdict after three hours of deliberation.

"Justice has prevailed, that's all," said Roberta Roper, mother of the 22-year-old art student who was awarded a posthumous degree magna cum laude.

After the verdict, the mother thanked C. Clarke Raley, the St. Mary's County state's attorney, who prosecuted the case. "You can't bring Stephanie back," Raley told reporters a few minutes later.

Jones was accused with Jerry Lee Beatty, 17, of murdering Stephanie Roper in the early morning hours of April 3. Beatty, scheduled to be tried separately next month, testified against Jones yesterday, asserting that his friend fired the shot that killed Roper and then set her afire. Under cross-examination, Beatty acknowledged his attorney had told him he would almost certainly escape the death penalty if Jones were convicted of firing the fatal shot.

The case was tried here in Baltimore County because a judge ruled that pretrial publicity might prejudice a defense in Southern Maryland.

The jury began deliberating today after two hours of closing arguments and rebuttal marked by lively sparring between Raley and E. Allen Shepherd, one of Jones' two court-appointed lawyers.

Raley accused the defense of "trying to insinuate" that Roper was "anything other than a most wonderful girl." Shepherd angrily denied this and accused the prosecutor of theatrics that he said "insult the jury's intelligence."

Raley made his closing arguments almost in a whisper, his voice rising only occasionally for emphasis, and he made use of the murder weapon, a .22-caliber rifle, and a logging chain with which Roper was struck.

Saying at one point that Jones had hit her with the chain, the prosecutor swung it in the air, almost striking Shepherd, seated nearby. Raley also brandished the rifle as he described evidence that he said showed Jones had shot Roper once in the forehead when she tried to escape.

Raley said Roper had been subjected to the "most violent, unmitigating terror" imaginable, as the two men who first offered her assistance failed to return her to a friend's home as promised, then drove her to an abandoned house near the Patuxent River, repeatedly raping and eventually killing her.

The prosecutor referred to the two men, including his star witness Beatty, as "two alleged people" who "do not truly belong to the human race." He asked the jury, "Who can think in terms of any kind of justification, mitigation, excuse? Are we fools?"

Noting that Jones had allegedly borrowed the rifle from a friend to hunt deer, Raley referred to Roper as a "disoriented doe or fawn" when, staggering from the blow of the logging chain, she attempted to flee her abductors.

"The very day the young fawn is killed," Raley said, Jones and Beatty had a "macabre, inhuman discussion" of mutilating her remains to prevent identification. "If you have not committed the most heinous crime, no thought is given to such inhumane things," Raley said. Police found the body on Easter weekend, missing both hands.

Shepherd sought to impeach Beatty as an unreliable witness who had lied to police, to a state psychiatrist and to the jurors. He called him a "cold, selfish person with probably no conscience at all, who would lie for his own benefit."

Beatty was "very likely the person who shot Stephanie Roper when Jack Ronald Jones wasn't present," Shepherd asserted, consistent with his client's statement to police that he struck but never shot the woman.

After the verdict, Circuit Judge Walter R. Hail scheduled testimony to begin next Wednesday on whether Jones should receive the death penalty. Jones may leave the decision to the jury or elect to have the judge determine his fate.

After the jury was dismissed and given a sheriff's escort past the television cameras, Roberta Roper thanked a dozen or so friends and neighbors who had regularly attended the trial. We wouldn't have made it through this week without all of you." said Roper, who lives near Upper Marlboro. "So, from Steffie and everyone in Steffie's family, thanks."