Closing Arguments Heard in Slaying Trial : Justice: An attorney argues that his client did not know that the man he shot was a police officer.

If an undercover police officer was able to conceal his identity for 10 hours from a burglary suspect he had under surveillance, a gunman who killed the officer in a brief shootout at the stakeout scene also could not have known who he was, a defense attorney argued at the gunman’s murder trial Tuesday.

Attorney Marvin L. Part said during closing arguments in San Fernando Superior Court that Louis Belvin Jr., 22, of Los Angeles shot undercover Officer James H. Pagliotti, 28, in the belief that Pagliotti was a disgruntled drug customer attacking him with a gun.

Belvin and a friend, Thomas Lee Mixon, 23, also of Los Angeles, had been selling drugs on a Sylmar street corner on June 22, 1987. Shortly before the shooting, Belvin and Mixon had beat up a customer who returned to complain about the quality of cocaine he had purchased from them.

Pagliotti was part of a team of undercover officers in rental cars who had been watching a burglary suspect in the area for nearly 10 hours. Pagliotti was dressed in shorts and a print shirt and was driving a white Toyota.

Pagliotti and other officers “had done everything they could to fool a master criminal, but when Belvin comes around, he’s supposed to know that Pagliotti was a cop,” Part said.

“Morally, what the defendant did was wrong, but legally what the defendant did was right,” Part argued, saying the jury should find that the shooting was in self-defense.

Another undercover officer in the surveillance team saw Belvin standing in the street holding a gun, and thought that he and Mixon were about to commit a robbery. He put out a radio call, and Pagliotti was the first officer to respond.

Several police officers who arrived as shooting began testified that Pagliotti identified himself as a police officer and that Belvin fired the first shots.

However, Belvin testified that he was sitting on a planter in the front yard of a house when Pagliotti slowly drove up, got out of his car and pointed a gun at him without identifying himself. Belvin said he then ran down the street and Pagliotti shot him in the back. Belvin said it was only then that he turned and fired three shots at Pagliotti, one of the shots fatally wounding the officer.

Part said there was no reason for Belvin to believe that Pagliotti was a police officer. Part said the shooting was the result of a series of mistakes and miscalculations made by the undercover officers.

But Deputy Dist. Atty. Susan M. Speer told the jury that the only mistake was in Part misinterpreting and misquoting testimony in the case. “If you believe Mr. Part,” she said, “then almost every single witness is lying except Belvin.”

The jury is expected to begin deliberating the case today.