Alexandria's Public Safety Department began an internal investigation yesterday into attempts by one or more police officers to block radio transmissions by a police investigator during the past week.

"The deliberate and potentially dangerous interference cannot and will not be tolerated," said Acting City Manager Vola Lawson, who requested the investigation.

Both Lawson and Public Safety Director Charles T. Strobel called for modifying the police radio system, either with a monitoring system or an emergency override capability, to prevent "jamming" transmissions.

Strobel warned his staff in a memorandum yesterday that the offending officer or officers would be liable for disciplinary action, including possible criminal prosecution. Virginia law punishes interference in two-way radio communication with either a $1,000 fine, 12 months in jail or both, police said.

"This is a deplorable and illegal action that could cause serious consequences," Strobel said.

The investigation came after two incidents in which radio transmissions by investigator Joseph Morrash were blocked.

Many in the police department have said they believe that blocking Morrash's radio transmissions is linked with his recent actions that included introducing motions of no-confidence in Strobel and the police department at the last meeting of the Alexandria Police Association.

Morrash also was one of two officers who successfully sued Strobel in July. A U.S. District Court jury found that Strobel had violated the constitutional rights of Morrash and officer Morton Ford when he transferred them from investigative to patrol duties for punitive reasons in 1983.

According to Morrash's account of the incidents, which has been confirmed by police officials, when he was working off duty as a security guard last Thursday, Morrash tried to transmit the description and location of a larceny suspect. Police at the time were looking for a man who had just burglarized a Sears store at the Landmark Shopping Center and had been seen in Morrash's vicinity.

Morrash made three attempts to relay information to other officers, but each time his transmission was cut off because another officer depressed a microphone key.

"My intention was to get to the [suspect] and ask who he was," Morrash said. "I'm glad now that I didn't get to him; I would not have been able to call for a backup. This is the first time I've seen someone deliberately covered. They knew someone was coming my way."

Police never caught the larceny suspect.

A second incident occurred Wednesday afternoon, when Morrash attempted to make a routine call to another officer and again was prevented when another officer "covered" his transmission, said Deputy Director of Public Safety John V. Streeter, who is in charge of the investigation.

" [After the first incident] they took a wait-and-see attitude," Morrash said of the department. "What are they going to wait and see, me lying face down on the pavement? Hopefully, the investigation will cause a deterrent."

"It could have been accidental," Streeter said of the second incident. "I believe it was deliberate."

Streeter said that several names have surfaced in connection with the two incidents.