A convicted murderer and bank robber, wearing pajamas and with his legs bound with chains, yesterday escaped from the custody of a D.C. Corrections Department guard about 20 hours after he had been found guilty of an escape last August from the new D.C. jail.

Police and Corrections Department officials said Ralph Walker, 28, overpowered the guard at the D.C. General Hospital, where he was undergoing court-ordered medical tests.

Walker grabbed the guard's gun, commandeered a nurse's car in the hospital parking lot and eluded several pursuing police cars, law enforcement officials said.

Walker was still at large last night, but D.C. police and FBI agents working on the case said they had located the nurse's car abandoned in Southeast Washington. They would not specify the exact location where the vehicle was found.

Walker, who is serving a total of 55 years in prison sentences in connection with the murder of an Alexandria policeman during a bank robbery four years ago, was brought to D.C. jail last August as a prospective witness in a murder case here.

He was one of four persons who escaped from the new jail on Aug. 26 by sawing through the frame of a window and sliding down tied-together bedsheets to freedom.

Walker was arrested on escape charges last December at 39 Mississippi Ave. SE, and went to trial before U.S. District Judge Oliver Gasch last week.

Walker served as his own lawyer during the trial and attempted to prove that he was forced to leave the jail because of the poor conditions there, and because he was an epileptic who was not receiving proper medical care.

Walker collapsed twice in the court-house during the trial, and on one of those occasions pulled a lectern on top of himself as he fell.

Assistant U.S. Attorney Steven R. Schaars questioned the legitimacy of these alleged seizures, and doctors who examined Walker at the court-house said they could not conclude whether the attacks were real or feigned.

After Walker collapsed in front of the jury, Judge Gasch ordered him to undergo testing in D.C. General, where the Corrections Department operates a locked ward.

Walker was convicted by a jury about 6 p.m. Monday as were two codefendants, Clifford Bailey and Ronald Clifton Cooley -- on the escape charges.

Around 2 p.m. yesterday, Walker was being taken from the third floor of the hospital to an X-ray room when he overpowered guard Dan Grady near an elevator. During a scuffle, Grady's gun fell to the floor and Walker grabbed it, according to police.

He managed to hobble to the elevator, out a hospital door and to a hospital parking lot where he threatened nurse Peggy Kornegay and told her to leave her keys in her car, police said.

Walker fled the hospital area in the nurse's brown 1972 Plymouth with District of Columbia license tags, police said.

Walker, who referred to himself during the trail as Walker-El and Walker-Bey, also has been convicted of assault with intend to commit robbery and served a portion of a 40-month to 10-year jail term on that charge.

Walker was convicted in Alexandria in June, 1973, for the December, 1972 murder of Alexandria Detective Conrad L. Birney. Birney, 40, a city youth bureau detective, was shot during a holdup of the Seminary Plaza branch of the United Virginia First and Citizens Bank in Alexandria.