On the eve of contract negotiations with the town, Tisbury police chief John Cashin yesterday mounted an extraordinary attack on dissident members of his own department, threatening to sue some officers for defamation over a whispering campaign against him.

He also accused one of the selectmen — whom he declined to name but who was identified by several other sources as Jeff Kristal — of undermining his authority by interceding on behalf of an officer Chief Cashin wanted to discipline for abuse of sick leave entitlements.

In an interview with the Gazette yesterday, Chief Cashin said a handful of police had worked to undermine him ever since his appointment two and a half years ago, and had spread “vile, preposterous and outrageous” rumors about his sexual preferences, including an alleged sexual advance to a male officer, substance abuse, and his sanity.

He said five members of the 13 strong force were involved, that the department was now totally dysfunctional, and that his tenure in the job had been dominated by “putting out personnel fires” and dealing with difficult and resentful members of the force.

The revelation last week that the department’s only female officer, Kelley Kershaw, had lodged a complaint of sexual harassment and discrimination with the Massachusetts Commission Against Discrimination, he said, had only added to tensions that had existed in the department for years before he was appointed police chief.

His scathing attack on some of his own officers and his criticisms of the board of selectmen for lack of support and unwanted meddling foreshadow a difficult time today when he meets the board beginning at noon.

The meeting, which was scheduled before his outburst, was intended originally to be a routine start to formal negotiations over his appointment as chief for another three years.

Mr. Cashin was sworn in on Sept. 5, 2006. Under the terms of his contract, if the board does not plan to renew his contract they need to notify him three months in advance of the third anniversary of that appointment, which is June 5.

But his future may well be decided today.

“I think the time has come to deal with the personnel issues that have been plaguing this department for years, from what I understand,” he said yesterday.

“I heard a month after I got here this one particular sergeant was saying ‘I’m not concerned about the chief, the chief’s office has a revolving door. He’ll be out of here in three years.’

“My message is, if the selectmen want that, fine. However, they’d better be prepared for it to happen to the next person as well. Because they’re giving the inmates total charge of the asylum.

“I would like the support of the selectmen in that. And if they will have me, I will stay, and that will send a message to these officers that they are not empowered to evict a chief. That they are going to do their jobs and there will be strong changes here,” Chief Cashin said.

He said he was contemplating legal action, regardless.

“I know it might sound incredible or outrageous that a chief would sue an officer, but at this point I’m very concerned about defamation of character and what it will do to my future, whether or not I stay here.

“I don’t know, if we [the selectmen] reach some agreement about what’s going to happen and it’s somewhat mutual and amenable to both parties, if that’s going to stop any potential lawsuit.

“Because quite honestly, I have never been treated so disrespectfully in my entire life, in relation to either my professional or personal conduct.

“There’s crap out there that is so outrageous and unbelievable: substance abuse, sexual advances, I’m gay, I’m crazy. There is even a story out there that I was running around town the other night, waving my gun around.

“To a guy in my position, that’s kind of harmful,” he said.

And the rumors were not circulating just within the department.

“I have been contacted by people at the court who have told me different things. I got a call from a reporter yesterday [Wednesday] seeking to confirm what he had heard in Edgartown, that I resigned.

“By no means is it all the officers,” Chief Cashin said.

“Tisbury has some very caring, compassionate and committed officers. Unfortunately they also have some officers who are, I don’t know, burned out or bitter about something, but they have attacked me beyond all reason and just with an acerbic attitude since the day I came on.

“We’re talking about five people, who have gone out of their ways to undermine, to back-door, to back-stab. They never took the opportunity to give me a chance, these officers.”

He said that some other officers had approached him to say they were prepared to come forward and vouch for him, if necessary.

“That means a lot to me, but I would never ask them to do that, because, win, lose or draw, they’ve got to stay here,” Chief Cashin said.

As to the dissidents, he said: “I never anticipated this type of hatred and really there’s no word I can use that conveys the bitterness. They’re not just malcontents; they’re destructive.”

“I didn’t come up here to punish people and start kicking ass and taking names. That’s not my way,” he said.

Chief Cashin recalled with some irony that when he was interviewed for the job, one thing the selectmen stressed was the need to bolster morale in the department.

And it was widely held that he was an ideal candidate, given that he holds two masters degrees, in criminal justice and counseling, trained as a peer support officer for his department in Norwalk, and had a reputation for people skills and being a strong communicator.

“If anything, I came in here kind of meek and quiet, and that obviously doesn’t work here. The more giving, the more forgiving I was, the more they took advantage.”

Despite all the bitterness, though, he said he felt the department could be made functional again, with “some extraordinary discipline, a reinstatement and stringent enforcement of policy and procedure.

“But ultimately there are some of them that we would be much better not having here,” he said.

A major factor in Chief Cashin’s decision to go public with his frustrations appears to be a belief that at least one selectman was ready to move against him.

“I recently started to take action against an officer — who is problematic at best — and who was abusing sick time. And one of the selectmen got involved and it was inappropriate and we had words.

“I was made to feel quite insulted and rather foolish by that intervention. There were some hard feelings.

“Then I was informed — not from him directly, but from a reliable source — there was talk that my contract would not be renewed.”

“At any rate I figured it was time to do something here,” he said.

Yesterday Mr. Kristal initially refused comment on Chief Cashin’s allegations of interference by the selectmen.

“We have a meeting tomorrow at 12 noon and I will give the chief the respect that he is due, to sit down and discuss issues with him in private, rather than air it in public,” he said, when first contacted.

Later in the day, after it was put to him that several sources had identified him as the selectman about whom Chief Cashin was speaking, he said more, although he refused to confirm or deny his involvement.

“The first responsibility I have is to the voters of this town. And if the selectmen have concerns coming from the voters, the people of this town, then it is our responsibility to bring those concerns to the chief.

“I don’t consider that micro-managing, but managing.

“We are in a town administrative form of government here. And if somebody comes from a different system than we have in place on the Island then that’s a conversation that needs to be had.”

Fellow selectman Tristan Israel would say only: “We do not get involved in the day-to-day management of the police.”

Former selectman Denys Wortman, who was one of those who appointed Chief Cashin, said he thought the turn of events was “a real shame.”

“I think rumors have run rampant. I think there are a lot of people who love to talk,” Mr. Wortman said.

“John and I have always had a good, friendly relationship. I think the chief, basically, is a really good person. But he is feeling a high level of frustration with all that was going on.”

And the man who replaced Mr. Wortman on the board at last month’s election, Geoghan Coogan, also acknowledged rumors and insinuations.

“There’s a lot of stuff going round,” he said.

“I think everybody needs to take a collective deep breath and let the process work itself out,” Mr. Coogan said. “The chief is obviously frustrated, but we’re going to meet tomorrow to work this out the way it should be worked out.”