Boston public school teachers voted late last night in a secret ballot to accept a new contract offer from the Boston School Committee, averting a threatened strike by thz 5500 teachers today.

Henry Robinson, president of the Boston Teacher's Union, had recommended that the teachers reject the contract offer and predicted after a voice vote and show of hands earlier yesterday that the secret ballot vote would call for a strike.

Decisive

The final vote tally in the secret ballot was 1708 to accept the contract and 1353 to reject it.

David I. Finnegan, Boston school committee president, said yesterday the committee had met many of the teachers' demands on health and welfare benefits. The key issue remaining yesterday afternoon was class size.

Contingency Plans

School Supt. Robert C. Wood had said before the vote that administrative personnel and substitutes would staff Boston classrooms this morning if teachers voted to strike.

An announcement was expected from the administrators' union, however, stating that its members would not replace teachers in Boston's classrooms.

More Strikes

In Fall River, teachers who have been on strike since Sunday decided yesterday to ignore a judge's order that the 850 teachers return to work today.

Cafeteria workers in Fall River yesterday refused to cross the teachers' picket lines, and school officials told students to bring lunches to school as the officials tried to keep schools open at least through this week.

A two-day teachers' strike in Chelmsford ended yesterday and teachers returned to the classrooms after reaching a tentative agreement with the Chelmsford School Committee.