An off-duty Philadelphia police officer who tried to stop a murder in February on North Broad Street testified yesterday that he saw the victim being stabbed "at least 10 times."

Officer Jason Sommerville recounted driving down Broad Street about 2:30 p.m. on Valentine's Day when he saw Howard Cooper chase Matthew Bullock into the median near Huntingdon Street.

"He hit him [Bullock] once, and he was down," Sommerville told Assistant District Attorney Joanne Pescatore, adding that he saw Cooper strike Bullock in the face twice with his fist. "After the initial hit, I saw a silver knife in his [Cooper's] hand."

Sommerville testified during a preliminary hearing for Cooper, 47, of Southwest Philadelphia, who is being held without bail. Cooper, his hair and beard trimmed, and wearing a green T-shirt, sat silently throughout the proceeding.

Sommerville said that as he rushed from his car to aid the victim, who was curled up on the ground with his hands over his face, he saw Cooper stab Bullock all over his body.

Gun drawn and dressed in blue jeans, tan boots and a black police flight jacket issued by the Office of Homeland Security, Sommerville yelled, " 'I'm a police officer - drop the knife!' " he testified.

"He just looked at me," Sommerville said. "[Then] he started to do a slow backpedal, and then he started to run."

Sommerville chased Cooper across Broad Street into a vacant lot where Cooper "turned, squared [off] with closed fists, one holding a bloody knife."

Sommerville testified that he slammed Cooper to the ground with his left hand and that they struggled briefly before Cooper rose, transferred the knife to his left hand, then tossed it aside.

Sommerville testified that Cooper repeatedly said: " 'I tried to kill that motherf------, I'm gonna kill you, too, and I'm glad cops are being killed.' "

Pescatore said authorities knew of no motive for the killing of Bullock.

Dan Stevenson, one of Cooper's defense attorneys, said in a phone interview with the Daily News that Cooper and Bullock were acquaintances.

"There was a confrontation immediately before the event the police officer saw, where Bullock was the initial aggressor, and threatened him with a knife," Stevenson said.

"Our client was himself attacked," he said. "It was self-defense."

After the initial struggles, Sommerville said, he again forced Cooper to the ground. A passer-by offered him a phone to call 9-1-1. Sommerville said that when he told the operator that he had a criminal in custody, Cooper yelled, " 'I'm not in custody yet,' " and started fighting again.

Cooper, who has a lengthy arrest record, told him: " 'I did 22 years. I'm not afraid of going back,' " Sommerville testified.

Police officers soon arrived and took Cooper into custody.

Bullock was taken to Temple University Hospital, where he died at 6:03 p.m.

Municipal Judge Jimmie Moore set an arraignment in the case for June 23.