Cambridge teachers began an "informational picket" campaign in front of city schools yesterday, hoping to gain concessions in their stalled contract talks with the school department.

Marie Orben, president of the Cambridge Teachers Association (CTA), could not be reached for comment yesterday, but a message on her answering machine said teachers met in front of at least three city schools yesterday morning, then marched in together before classes began.

"We only went out this morning," said Robert Richards, a member of the union's board of directors. He said the picketing was "fine" this morning. But Richards would not comment further on the teachers' plans and referred all further questions to Orben.

The pickets took place in front of the Harrington and Longfellow schools as well as Cambridge Rindge and Latin High School, according to Orben's telephone message. The CTA also aired radio commercials on at least six stations, according to Orben's answering machine.

3 Weeks, No Contract

For two weeks CTA representatives and the school department have met with a mediator to break the eight-month-long deadlock in contract negotiations, city officials said. The Cambridge teachers' contract officially ran out August 31, and, according to city officials, they agreed to work under the old contract until a new one is approved.

According to recent news reports, Orben noted that teachers' strikes are illegal when asked if the union would strike.

The school committee is offering the teachers a 3 percent raise for this year and 4 percent next year, said the school department's director of public information, Albert H. Giroux. But he said the teachers demand an 8 percent raise for this year and subsequent 9-1/2 percent and 10 percent raises for the following two.

While agreeing that teachers should be paid more, school committee members said they cannot afford to provide the teachers with an 8 percent raise. Teachers' salaries already make up four-fifths of the school budget, they said, adding that the department must pay health insurance costs, special needs education costs, and automatic raises based on teachers' seniority and coursework.

"We would like to see the teachers well paid, but we don't have the money," said fifth-year school committee member Frances H. Cooper.

Giroux said many changes, unrelated to the current contract talks, took place during the summer. Both Superintendent Robert J. Peterkin and the assistant superintendent Dr. Barbara Marshall, took more prestigious jobs in the Milwaukee school system. In addition, the principal of one of the elementary schools accepted a job as head of Harvard's Principals program.