Michael Orlando could be your next-door neighbor.

He graduated from St. John's University. He has a wife and three children. He used to teach grammar school on Long Island.

But there is something that distinguishes him from your ordinary grade-school teacher. According to a tape recording played in court today, he matriculated as a hit man for the Mafia.

"This . . . is a bad kid, you know, this kid Mike," Orlando's onetime employer, William P. Masselli, told a visitor to his South Bronx meat plant on March 8, 1979.

"When I say he's a bad kid, forget about it. He knows it. This guy's got about 10 under his belt already, in case you don't know it."

FBI monitors conducting an organized crime surveillance of Masselli's plant recorded every word, the court was told today in connection with the case against former U.S. labor secretary Raymond J. Donovan, Masselli and eight other men.

The chief monitor, FBI agent Robert A. Levinson, testified that there was "no doubt in my mind, sir," that Orlando was being credited, in gangland parlance, with 10 murders.

Levinson also conceded, under cross-examination, that the FBI failed to include any mention of the allegation in its daily log or in the periodic reports to the federal district judge in charge of the surveillance.

The judge was told other details about the conversation, including the "bad kid" remark, but that was all.

Defense lawyers contend that the omissions stem from the fact that Orlando was also a $500-a-week FBI informer who had been the key to getting court approval for the surveillance.

And they contend that the tape recordings -- now the principal evidence in the Donovan case -- must be suppressed because of the FBI's alleged failure to inform the court, and the Justice Department, of Orlando's criminal activities.

In his seventh grueling day on the witness stand, Levinson said he went by the books and treated Orlando "like any other subject" overheard during surveillance.

But Levinson plainly had to walk a tightrope because he was the only FBI monitor who recognized Orlando's voice from the outset and knew that he was an informer.

Levinson said he remembered the March 8, 1979, conversation clearly, but another FBI agent was compiling the logs that morning and perhaps skipped over it.

Feeling "a duty" to protect Orlando's status as a secret informer, Levinson said that he told only one other FBI man, Lawrence Sweeney, who had recruited Orlando, about the "10 under his belt" remark.

Asked why he didn't report it to FBI higher-ups, Levinson said he would have done that "if there had been a specific reference to a murder."

But he said, "Masselli's reference to '10 under his belt' -- that's not unusual."

Levinson said he did ask Orlando himself "whether he had 10 under his belt" at some later date.

"I asked the gentleman whether he committed any murders. He denied it," Levinson testified. "I had no specific homicide to investigate."

Orlando has since admitted that he was the gunman in the Sept. 22, 1978, gangland slaying of a mobster named Salvatore (Sally Blind) Frascone.

But there has been no suggestion that his FBI handlers knew about that until years later when Orlando entered the federal witness protection program.

The FBI agents who dealt with Orlando continued to contend that, whatever his morals, he was an invaluable informer.