Two police officers fired about 20 shots at a vehicle that struck and injured one of the officers early yesterday morning in Old City, the latest mayhem to break out around Philadelphia's nightclubs.

Internal Affairs investigators are looking into officers' use of force after the encounter in the 100 block of Chestnut Street, the same block where there was a fatal gun battle three weeks ago.

Yesterday's violence broke out about 2 a.m. after a SEPTA police officer stopped a black SUV that had cut off the officer's patrol car, said Lt. Michael-Jerry Lee of the Central Division Detectives.

After the transit officer got out of his car to approach the SUV, the vehicle "started backing up as though trying to flee the scene," Lee said.

Fishtailing on the slick street, the vehicle struck a Sixth District Philadelphia patrolman who had walked into the street to assist the SEPTA officer, Lee said.

The officer - part of a detail assigned to patrol nightclubs after three fatal shootings in the last six weeks - was briefly pinned against a parked car.

Then, as the vehicle started to move away, the two officers fired about 10 shots each, striking the SUV numerous times, Lee said. The SEPTA officer was the first to fire, Lee said.

The occupants of the vehicle did not return fire, Lee said, and no guns were recovered.

The city police officer was treated and released from Jefferson Hospital with "minor injuries" to his shoulder and leg, Lee said. The SEPTA officer was uninjured. Neither was identified.

A black Ford Expedition with its rear and side windows shattered and numerous bullet holes in its body later was found at the Hospital of the University of Pennsylvania. Police questioned two men with minor gunshot wounds but did not charge them.

"These two were just passengers," Lee said. "They didn't have control of the vehicle."

He said two or three other occupants of the vehicle, including the driver, apparently fled.

The vehicle was impounded and searched, Lee said.

Internal Affairs investigators are examining the officers' use of deadly force, as they do with all cases in which police fire their weapons, said Lt. Frank Vanore, police spokesman.

Though Philadelphia police officers are permitted to use deadly force "to protect themselves or another person present from imminent death or serious bodily injury," they are severely limited as to when they can fire on a moving vehicle.

"Police officers shall not discharge their firearms at or from a moving vehicle unless deadly physical force is being used against the police officer or another person present, by means other than the moving vehicle," states the Police Department directive on deadly force.

"If they felt their life was in danger, either with the vehicle moving toward them or with an officer pinned, that'll be a determination of the investigation," Vanore said.

The transit police subscribe to the same rules on the use of deadly force, SEPTA spokesman Gary Fairfax said.

The shooting was the latest outbreak of violence around Philadelphia's club scene.

On Oct. 28, police shot and killed a gunman outside Koko Bongo in University City after the suspect shot a police officer and injured a bystander.

On Nov. 18, one man was killed and another injured when a gun battle erupted outside Dreemz, a club on the same block of Chestnut Street where the shooting took place yesterday.

On Nov. 26, University of Pennsylvania police killed a gunman in Club Wizzards at 38th and Chestnut Streets.