A Prince George's County jury convicted a man yesterday of murdering his girlfriend by shooting her on a busy Upper Marlboro on-ramp to Route 4 in a brazen midafternoon attack.

After deliberating for about four hours, the Circuit Court jury convicted James H. Pierce Jr., 58, of second-degree murder and using a handgun in a crime of violence in the slaying of Towana Lee Folk. It acquitted Pierce of first-degree murder.

Pierce, of Upper Marlboro, faces a maximum sentence of 30 years for the murder conviction and 20 years for the handgun violation. Circuit Court Judge Thomas P. Smith has scheduled sentencing for Jan. 13.

Pierce's defense attorney, Tara Harrison, declined to comment. She told jurors in her closing argument yesterday that Pierce could not form the intent to commit murder because he was incapacitated from a crack cocaine binge.

During the four-day trial, Assistant State's Attorney Fran Longwell presented evidence that Pierce, driving a GMC truck, cut off Folk, who was driving a Nissan Altima, on the northbound ramp from Route 301 to Route 4 (Pennsylvania Avenue) about 3:20 p.m. Feb. 8. Folk was driving to Andrews Air Force Base, where she worked as a receptionist, relatives said.

After Pierce blocked Folk's path, he jumped out of his truck, walked up to the driver's side of her car and fired six shots into her, Longwell said in her closing argument yesterday.

"He executed that woman. She didn't have a chance to do anything," Longwell said.

Folk, 48, of Upper Marlboro, was taken to Southern Maryland Hospital Center, where she was pronounced dead.

Police found an incriminating letter from Pierce in Folk's purse, in the passenger seat of her car, Longwell told jurors. The letter, which Longwell read for jurors, said in part: "I asked you to stand by me; you are all that I have. I asked you to forgive me, but you reject me." The word reject was underlined three times.

The letter ended, "I LOVE YOU!! god forgive me . . ."

Longwell read a second letter, to a relative, in which Pierce apparently described his own suicide, writing, "I took the pills on my own." The letter also said he was going to hell for what he had done.

Folk "told him she didn't want him in her life, and he couldn't deal with it," Longwell told the jurors.

Whatever his intentions, Pierce did not try to commit suicide.

After the shooting, Folk's teenage daughter told police that Pierce carried a revolver, a Prince George's homicide detective, Kelly Rogers, wrote in a charging document. Rogers wrote that she made an appointment to interview Pierce several hours after the attack but that he did not keep the appointment and could not be found.

One of Pierce's adult daughters told Maryland State Police that her father had gone to Philadelphia. At the request of investigators, the daughter arranged to meet him, and Pierce was arrested by Philadelphia police.

Rogers obtained a written statement from Pierce and a videotaped statement. In the videotape, which Longwell played for jurors, Pierce addresses Folk's daughter, who was 17 at the time.

Pierce begins by saying he is "assuming full responsibility" for what happened to her mother. "By me talking to the detectives, a burden has been lifted off my shoulders," Pierce said.

Pierce claimed that Folk used crack with him, but a toxicology report found no cocaine in her system.