The MBTA's third and latest plan to move the Bennett Street transit facility and expedite construction of the Kennedy Library has been sharply criticized by the chairman of the Milton Board of Selectmen as "uneconomic and unwise."

The $12 million plan, revealed February 1, includes replacing trolley service between Ashmont and Mattapan with a rapid transit line, closing three stations in Milton, and building a new maintenance and storage facility in Mattapan Square for 100 cars.

In an interview last night, Chairman Francis F. Brooks '37 said that his board will present a letter today to MBTA General Manager Leo J. Cusick blasting the plan.

The opposition of the Milton selectmen could play an important role in further delaying construction of the library. Already, two far less expensive MBTA sites have been abandoned in the past year because of strong local opposition.

Marshland

The second site, on a marshland between Milton and Dorchester, was proposed last December by Governor Volpe. But Milton selectmen and Dorchester state legislators raised an outcry against it, and Volpe dropped the issue.

The plan must receive the approval of the MBTA's five-man Board of Directors, which meets Thursday, and of the MBTA's Advisory Board, which meets next week.

According to a Kennedy Library spokesman, the Mattapan site has some important advantages over the others:

* The line and storage facility are needed now anyway--Kennedy Library or not--to speed up service.

* No legislation is needed to put the plan into operation.

* In the long run the MBTA will save money by using Mattapan, since it will be a permanent facility and the others were merely temporary.

* Only one-quarter acre of land will have to be acquired.

Brooks, however, is not satisfied with these arguments. He said that closing three Milton stations would inconvenience a large number of people, the cost of the plan would mean unnecessarily increased tax assessments, and running rapid transit into an area where only 1500 people board per day is wasteful.

"We are being given a runaround," he said. "Frankly, our people are disgusted."

Brooks added that he is certain that Cusick would never have made the proposal "were it not for Bennett Street and the Kennedy Library.