The officer, Scott Schweizer, heard a noise in the back yard of his Northeast Philly home at 1:59 a.m. When he peeked outside, he saw three men standing in his fenced-in back patio. The unidentified suspects fled when Schweizer yelled at them, according to police spokeswoman Officer Tanya Little.

Schweizer then ran outside and discovered the letters "KKK" scrawled in blue paint on his back door, and "die pig" emblazoned on the white aluminum siding. The door frame appeared slightly damaged, and Schweizer believes that the men tried to break in, Little said.

Schweizer, 33, is in the middle of a racially charged firestorm and is the subject of an ongoing Internal Affairs investigation.

The probe began in January, when two incendiary stickers were found inside his police locker. One sticker read "White Power." The other depicted a cartoon of a man - half of him an officer in uniform, the other half a Klansman - with the words "Blue By Day - White By Night."

Schweizer has been removed from his undercover police duties and given a desk job, pending the outcome of the internal investigation.

As a member of the force's elite Narcotics Strike Force, Schweizer has arrested hundreds of suspected drug dealers in predominantly black neighborhoods. Defense attorneys are now challenging Schweizer's cases in court.

Schweizer's attorney, Allan J. Sagot, has claimed that his client was the victim of a tasteless practical joke. Sagot said that another officer slapped the stickers on the outside of Schweizer's locker and Schweizer, without thinking, quickly ripped them off and pasted them on the inside to shield them from view.

Yesterday afternoon, a manned police cruiser idled in the back alley outside Schweizer's home as a protective measure.

"We're very concerned about the safety of police officers and their families in their homes," said John McGrody, a vice president of the Fraternal Order of Police, Lodge 5.

Schweizer, who was home when a Daily News reporter came by, did not answer his front door or respond to a note left for him.

"What can I say?" Sagot said yesterday. "It's a terrible thing."

Schweizer, who filed an incident report with police, told an investigator that he did not get a good look at the graffiti culprits and could not provide any description, according to Officer Little.

Rochelle Bilal, president of the Guardian Civic League, which represents 3,000 black officers in Philadelphia, questioned the validity of Schweizer's story.

"I would do a handwriting analysis first before making a decision that there was a crime committed," said Bilal, who declined to elaborate. *