A decision made by the trial court of Massachusetts to decrease the hours of the Vineyard juvenile probation officer has prompted concern from Island school officials and law enforcement personnel, who say they are worried about the long-term effects of the service reduction.

In letters sent to the trial court, Vineyard schools superintendant Dr. James H. Weiss and the Martha’s Vineyard Chiefs of Police Association note that the hours of juvenile probation officer Shawn Schofield would be reduced to two or three days per month. Officer Schofield, who has worked on the Vineyard for more than 18 years, will instead spend most of his time in Falmouth.

Dukes County Sheriff Michael McCormack said Thursday that Officer Schofield currently spends two to three days a week on the Vineyard, and one day a week on Nantucket. His Nantucket duties will be reduced to one day every other month.

Representatives from the state could not be reached by press time Thursday. Officer Schofield said on Tuesday he could not comment on the matter.

Sheriff McCormack said while researching a solution, he had found an overall shortage of probation officer staffing across the state.

“There are 200 positions in the commonwealth that need to be filled, so they’re very short-staffed,” he said. “Hopefully this will be a short-term issue, because Shawn has done such a terrific job handling the troubled youth of the Vineyard and Nantucket.”

He said Cape and Islands Rep. Timothy Madden had also written a letter of support for Officer Schofield. The police chiefs sent their letter on June 4. As of Thursday afternoon, Sheriff McCormack had not received a reply.

“Hopefully they’ll bring this issue before the legislature,” he said.

Mr. Weiss, the superintendent, said Mr. Schofield has had a positive impact in the public schools. “We — the schools, the police, the teachers, the parents — have a very good relationship with Shawn, and we avoid a lot of problems,” Mr. Weiss said. Officer Schofield is a member of the Vineyard Youth Task Force and a regular presence at district attorney monthly roundtable meetings. According to the police chiefs letter, he is also available for informal meetings with parents at the juvenile probation office in Edgartown.

Reached on Thursday, West Tisbury police chief Daniel Rossi said the probation officer spends a good deal of personal time working with families as part of an overall early prevention effort.

“With him not being here as much as he has been, I think a lot of the preventative measures that he has put into effect will no longer have as much [impact],” Chief Rossi said.

“He does a lot of proactive intervention with parents and troubled youth so that they don’t actually become a juvenile case that he has to handle,” Sheriff McCormack said. “Which doesn’t show up in anybody’s statistics, of course. So it looks like his case numbers are low, but they’re low because of his proactive activity.” Mr. Weiss said he was equally concerned with a trend toward reducing commonwealth services on the Vineyard in favor of shifting them to the mainland.

“I see a continued process of the Vineyard getting less and less service, and that just concerns me,” he said. “We have significant needs here, and if every [service] goes to Falmouth, those needs won’t be met.”