Alexandria city officials yesterday unmasked as a hoax claims by the city arborist that he had turned down elaborate bribes offered by area real estate developers and nurserymen.

When The Washington Star published arborist Gregory Kernan's comments last week, city hall officials and police detectives launched a criminal investigation. Kernan was given two lie detector tests in the probe.

Yesterday the investigation ended with announcement from the city manager's office that Kernan's statements were "total fabrications."

The 25-year-old arborist said in an interview yesterday that his comments were "just a joke."

"I thought she [the reporter] wouldn't print it," he said. "I was only kidding at the time."

Kernan was quoted in The Star as having turned down offers of cash, a week in the Bahamas and a house in Old Town - bribes allegedly offered by area businessmen in exchange for special treatment. In a subsequent interview, Kernan told a Washington Post reporter he could not identify the persons who made the offers and said he had not given the police any names.

Asked why he had continued the hoax, Kernan said yesterday: "I guess I had gotten myself too far into it."

Kernan also said that he was unaware at the time of the first interview that under Virginia law, attempted bribery is a felony punishable by as many as 10 years in prision.

Kernan, who earns between $15,000 and $20,000 yearly, was hired in 1976. His main duties are tree trimming, cutting, inspection and insect spraying.

Dayton Cook, the city planning and environmental services director who is Kernan's boss, said yesterday that the arborist would be "punished" but will not be "terminated."

"I don't know whether he was pulling the reporter's leg or inflating his own ego," Cook said. "We may never know."

"I'm not firing him," Deputy City Manager Clifford Rusch said. "But we may have to do some adjusting of his duties."

Kernan said yesterday that he believed the entire episode was "unfortunate" because it "added to the bad image of the city."

Capt. Andre Savas, head of the Alexandria police department's criminal investigation division, said yesterday he was relieved that the week-long investigation had ended, but "a lot of wasted man hours" that police spent on the case.

Arborist Kernan said the hoax had taught him three lessons: "First of all, never talk to a reporter. If you do, be careful what you say. And third, be honest."