I saw a cop shoot a guy Sunday night.

I watched it happen from the back seat of a New York cab, stopped for a red light at 96th Street and Central Park West.

The whole incident probably lasted three minutes. It seemed like an hour, with all the action and sound in slow motion.

"S---! DUCK!" the cabbie yelled. "We're gonna get hit!"

We didn't duck. We sat there glued to it all with some kind of frightened horror and morbid amazement.

In the end, 23-year-old Gilberto Polanco was sprawled on his back in the street.

He was lying right next to the night stick that 22-year-old transit police officer Charles Varrone had used before he pulled out his Smith & Wesson .38 special service revolver.

There was blood trickling from Polanco's chest and shoulder. I was shaking, half wishing to be somewhere else, half wondering if it could have been me.

When driver Irwin Furr pulled up to the light, we were heading south. We were talking about the Yankees -- Reggie Jackson to be specific. Furr seemed near my age, 33, and we had a lot in common.

I noticed a cop arguing with a guy on the southwest corner of the intersection, by the entrance to a subway station. They were dancing around each other like boxers, and yelling back and forth.

The guy threw a punch at the cop.

"What a dumb s---," I said to the cabbie. "The guy's hitting a cop."

The cop backed up into the street. He pulled out his night stick and his handcuffs. The guy came after him. They were about 20 feet in front of us now.

"Oh, no," I said. I was already wincing. "Somebody's gonna get hurt."

Furr was rolling up the front right window of the taxi.

"That f-----' cop is gonna shoot that guy," he moaned, almost in disbelief. "I can see it in his eyes."

The cop beat the guy over the head with his stick. He was pummeling him. The guy hit the ground. I don't know if he knocked the stick out of the cop's hand, or if the cop dropped the stick.

But the next thing I saw was the cop pulling out his gun. "Oh, s---," I yelled. I couldn't believe this was happening, and the way the cop was moving, we were right in the line of fire. That was when Furr yelled to duck.

The guy was still on the ground. It looked to me like he was starting to back off and raise his hands. He was getting up.

Pop. Pop.

It sounded like two little dull thuds. Puny and innocuous, like a toy gun going off. Nothing like the sound of gunfire in Westerns and cop movies or the noise on a pistol range.

The cop was running down the steps of the subway station now, yelling into his walky-talky.

"Do you want to get out of here?" Furr asked.

"We can't just leave the guy lying there," I said. But I was too scared to get out of the car.

So we sat and watched for a minute or two. I still didn't believe this had happened. It was too eerie. I had come to New York to write a profile on a cop named Bob Leuci, whose life story has been made into the film "Prince of the City." I wished this had been a movie. One that I could have walked out of.

Finally Furr drove off without waiting for me to say so. I was too shaken to object. I went to the home of some friends, and Furr gave me his phone number.

"This'll probably make all the papers," he said.

"Maybe," I said. "I'm a reporter."

At 9 o'clock on Sunday night, about 45 minutes after all this had happened, I walked back to the scene with my friends. There were a dozen cops there. I looked at the two blood spots on the street. I felt sick. I didn't know if the guy was dead or alive. I didn't want to know.

Yesterday morning the story was on the front page of the Daily News. The story said that, according to police reports, a man was shot twice and seriously wounded by a rookie transit authority cop. The man was in stable condition at St. Luke's Hospital. The cop was "pretty shook up."

Officer Varrone is on sick leave and under investigation. Assistant District Attorney Michael Ferguson said he will present evidence about the shooting to a grand jury within the next two weeks. This is all standard procedure in such incidents.

I called Ferguson and the transit authority police. I told them I was a witness and would cooperate.

Inspector Nicholas Cuccia, who is conducting the internal investigation for the transit police, told me that the officer said he was attempting to eject a panhandler from the station:

"The perpetrator took the officer's night stick and began to strike the officer about the head, neck and shoulder. During the course of this, the officer asked him to drop it, at which time the officer fired two shots. One struck him in the left shoulder, and one in the left chest area. That one exited from the back."

The way I remembered it, the "perpetrator" never got his hands on the night stick. So I called Furr at home yesterday afternoon.

"The cop hit the guy with the stick," Furr said. "From what I saw the guy was going for the stick when the cop shot him. But the guy didn't get a chance to hit the cop with the stick . . . Like I told you last night, I knew by the cop's face that he was going to shoot. He had that look on him even before he pulled his gun out . . . Any cop would have reacted the same way."