Last week a detective who helped solve an assassination murder of a cop 10 years ago was ordered to work a parade detail outside the stationhouse in Brooklyn's painfully notorious 70th Precinct. He was to stand at attention in his uniform, hands at his side, and protect the premises during a protest march.

Some of the protesters screamed the same curse Rudy Giuliani screamed at another mayor while standing at City Hall a few years ago with some of the same 70th Precinct cops he disciplined last week. As the detective stood, stone-faced, a part of him wanted to scream with the marchers. One fist was clenched against the insults in front of him; his other fist was clenched against the outrage behind him.

"I was humiliated by what people were yelling at me and ashamed of being seen as defending what happened behind me," he said.

More good cops will be caught in the middle at today's march, held to protest the inhuman treatment and humiliation of Abner Louima, who has taken a definite turn for the worse.

This city has two police forces: one small and horrible, and one great and noble. People see the uniform and figure all cops are part of the horror. That's not true.

In the 1820s, the city had two police forces, and they fought on the steps of City Hall. That police riot occurred when one force tried to arrest the mayor.

The closest we've come to that was when Giuliani encouraged a police mob to rattle then-Mayor David Dinkins in 1992. Giuliani no longer has that kind of support from the police. Morale is terrible, and most cops hate him.

When I interviewed Louima in Coney Island Hospital right before his torture and humiliation became national headlines, he did not say anything to me about Dinkins or Giuliani "time." He may have forgotten to mention it or I forgot to ask: "After the cops attacked you, did they say anything about Dinkins or Giuliani?"

In a later interview, however, he remembered the cops saying something else: "The black cops here are not going to help you, either. All they do is run the photocopy machine."

I have met Justin Volpe, the cop charged at the center of this, and his girlfriend, an administrative assistant at the 70th who chronicles arrests and works the copy machine. Was Volpe, who is white, driven by rage or racism? After seeing him with his intended bride, Susan, who is black, I could attribute the attack on Louima to rage.

"We were talking about where we were going to go on our honeymoon," Volpe said. "We talked about racism and cried when we thought of bringing up kids in this world. We talked about where we would live together."

"We had talked about living in Park Slope," Susan added. "Some place we wouldn't stick out."

Volpe was not, until now, regarded as brute in a precinct that was controlled by the police union until this year. Every station has a basher, a coward who gets brave once the handcuffs are on or beats prisoners in cells.

In the Bronx, there was a cop who was called in when someone wanted a prisoner beaten. This is part of the NYPD's brutal and sordid history. Only a mayoral puppet would call all this "anecdotal" -- whatever that means.

Police Commissioner Howard Safir, who thinks corruption is movie fantasy, will be framed forever by the Louima "anecdote." Giuliani is punishing a precinct commander who was on vacation during the attack on Louima but keeping a commissioner devoid of one original idea.

John Timoney, a former deputy commissioner run off in favor of "The Shopping Bag," as many cops refer to Safir, used to go to roll calls and tell the story of Nutsy Ryan:

"I used to be partners with the last cop in New York convicted of killing a prisoner. I volunteered to be his partner just to keep an eye on him. One night I missed work, and he killed a prisoner. If I had gone to work that night, I would have prevented the murder. Other cops allowed Nutsy to beat a prisoner to death. It isn't enough not to brutalize prisoners yourself. You have to stop it when you see it."

No one in the NYPD hierarchy has the credibility to have that kind of conversation. Chief Louis Anemone, whom Francis Livoti called "my cuz" until the bitter end, is worse than the commissioner.

Anemone leads by example. Two years ago, Anemone Maced several black men on Staten Island who were protesting police brutality. He should have been disciplined, maybe even arrested. No one said a word, which spoke loudly to the troops.

It is hoped that members of that other police force will leave their Mace locked up with their toilet plungers, mop handles and broomsticks today.