Convicted killer Jack Reynold Jones, facing a possible death sentence, testified for the first time today, saying he feels "deep remorse" over the murder of Frostburg State College art student Stephanie Ann Roper.

"It was a very cruel thing. I can't understand why something like that could happen," the 26-year-old St. Mary's County man told a Baltimore County jury charged with deciding his fate.

Jones and codefendant Jerry Lee Beatty, 17, were charged with the April 3 abduction, rape and murder of Roper, 22, after they happened upon her in her disabled car on a lonely Prince George's County road, a few miles from her parents' house in Croom.

Jones was convicted last week based in large part on the testimony of Beatty. Now that same jury will decide whether Jones should receive the death penalty, as sought by the prosecution. Jones' trial was moved here from southern Maryland because of pretrial publicity that a judge deemed prejudicial to the defense. Beatty is scheduled to be tried next week in Anne Arundel County.

Testimony during the trial showed that instead of dropping Roper off at a friend's house as promised, the two men drove her to an abandoned house in St. Mary's County near the Patuxent River, where she was raped, struck with a logging chain, shot in the forehead and set afire.

Speaking today in a low but controlled voice, Jones said, "I feel sorry as far as Stephanie's concerned and her family, her brothers and sisters, and I feel deep remorse for her family and for Stephanie."

His composure on the witness stand came apart only when asked about the impact of the crime on his own family. Turning his head to one side, Jones sobbed and shook for several minutes before saying that his mother is "very upset about what happened and she's concerned about my life."

As for his wife and 6-year-old son, Jones said, "I'm very sorry for what I've done to them and for what they're going through now. My son being without a father . . . I'm afraid what I've done is going to hurt him in life."

Jones was the final witness in this second day of the sentencing proceeding, which will resume next Wednesday. His testimony was intended to counter statements by Dr. Michael Spodak, a forensic psychiatrist who testified that Jones lacked remorse and could again pose a threat to society.

Spodak said that in a detention center interview, Jones had recited the facts of the crime to him "matter of factly. He could have been reciting a recipe," Spodak testified. "He seems to lack what you call a conscience in this area."

Although the psychiatrist found that such a "heinous act" was "uncharacteristic" of Jones, he challenged defense claims that it was unwillful and mitigated by Jones' heavy use of drugs and alcohol.

Jones, an eighth-grade dropout, portrayed his problems as drug- and alcohol-related and recounted what he described as an unhappy childhood during which he said his father often beat him.

He said he had been drinking since the age of 14 and using drugs such as PCP since he was 16. His drug usage rose sharply, he said, after he was laid off last February from his job as a maintenance worker at the Morgantown, Md., power plant.

"My wife used to tell me when I wasn't on drugs I was Jack, someone who cared, and when I was on drugs I was Bumper his nickname , someone who didn't care," Jones said.

With the victim's mother, flanked by her two teen-age sons, sitting in the front row, Jones then recited his version of the events leading to Roper's slaying. He asserted, as he had in a signed statement to police, that he did not fire the fatal shot.

"I thought I'd killed her when I hit her with the chain," he said, adding that he poured gasoline over her and lit the match after feeling no pulse. He said he then went to his home nearby and sat "gazing at the fire" in his fireplace.

"Since I've been in jail, I've turned to religion," he said. "My life's in the hands of the Lord. Whatever happens to me will be God's will. I feel He'll do what He feels is His will for me."