An investigation is under way into claims by a Tisbury policewoman that she was sexually harassed by a fellow officer and then subjected to retaliatory action from the police chief and town administrator when she complained about it.

In a detailed complaint, filed with the Massachusetts Commission Against Discrimination (MCAD) on April 28, Kelly R. Kershaw said she believed her alleged harasser, Sgt. Timothy Stobie, chief John Cashin and the town were trying to force her from her job.

Both sides of the story are not yet known, as police and the town have not yet responded to the claims. Following an executive session discussion of the matter by the Tisbury selectmen on Tuesday night, town administrator John Bugbee released a brief statement promising full cooperation with the MCAD investigation.

“I speak for the entire board of selectmen when I say that the town rejects any type of discrimination. We treat these claims very seriously and will handle the case accordingly,” Mr. Bugbee said in the statement.

In her statement of complaint to MCAD, Officer Kershaw claimed Sergeant Stobie began to sexually harass her about a month after he was promoted to that rank in February 2008.

“He harassed me on Saturdays because it was the day we were scheduled to work together,” she said, citing several comments of a sexual nature he allegedly made to her.

She also claimed that Sergeant Stobie made unwanted physical contact during the summer of 2008.

According to Officer Kershaw’s statement, she has worked in the Tisbury police department since August 22, 2004, and has been the only full-time year-round academy-trained officer employed there since that time.

Throughout her time with the Tisbury police, she said, she had received average or above average performance review results and had never been the subject of formal complaint or disciplinary action, until she rejected Sergeant Stobie’s alleged advances.

Officer Kershaw blamed him for the fact that she received a low score on her 2008 performance review, carried out in July and August of that year.

“I believe that because I rejected his sexual advances, he gave the chief negative feedback and Cashin never questioned it,” she wrote.

“It was during this review that I complained to Chief Cashin about the sexual harassment that Stobie was subjecting me to. The chief indicated he would talk to Stobie. The outcome was that Stobie was told that he will contact Cashin personally if he felt that I was in some way violating the rules of the department; but Stobie continued to subject me to continuous harassment,” she wrote.

On Oct. 26, Officer Kershaw submitted a written complaint to Chief Cashin and to the town, detailing the alleged harassment. No investigation was undertaken, she said, and following her complaints, there was retaliation.

“Stobie would yell at me or request that I do thing [sic] that male officers were not asked to do such as washing the cruiser in the middle of winter months, demanding that I go get his paycheck and scrutinize my written reports.”

Male officers, she said, were not treated in such a way or required to do such things.

Officer Kershaw also alleged discrimination in some rostering — she said she was forced to work overtime on Halloween when the duty should have fallen to one of two other officers.

Central to the complaint that the department and town were trying to force her out are events which ensued from an off-Island training program Officer Kershaw and another officer, attended in the last week of September.

The town paid for five nights’ accommodation for the officers in Portsmouth, N.H. Officer Kershaw apparently stayed in accommodations other than those arranged by the town, although the wording of her complaint leaves the circumstances unclear.

Later, when she and the other officer submitted their expenses, only those of the other officer were paid, and on Jan. 29 she learned that she was being investigated over the accommodation issue.

“Chief Cashin indicated he would file charges against me for larceny and terminate me for stealing from the town. He also stated that if I quit right now, then he wouldn’t investigate me and I could leave on my own terms,” she said in the complaint.

On Feb. 2, she said, she received a letter from Chief Cashin informing her she was under investigation, and would be interviewed.

But that interview did not take place, and 10 days later she received a letter of reprimand from Mr. Bugbee, for what her complaint described as “actions related to hotel stay on Sept. 26, 2008.”

Officer Kershaw’s complaint concludes: “I believe I was subjected to different terms and conditions, subjected to a hostile environment and retaliated against for complaining about sexual harassment. I believe that Stobie, Chief Cashin and the town are trying to force me out.”

A spokesman for MCAD said the respondents had been served with the complaint and an investigator appointed, but MCAD had not yet received statements from them.

If the investigation finds probable cause, the MCAD process provides for mediation, before proceeding to a public hearing.