Cambridge public schools yesterday began observing the new law for voluntary prayer in classrooms, after the School Committee voted last week to obey the law.

Some teachers offered a voluntary prayer time yesterday, although several students said that their instructors ignored it.

Optional Mandate

Arthur Lipkin, a teacher at the Cambridge Rindge and Latin School, said he plans to ignore the law because "offering the option (to pray) is tantamount to inviting it." He and about 50 other teachers have signed a petition declaring that they will not offer a prayer period in their classrooms. If any disciplinary sanctions are enacted, Lipkin said that he will face the consequences.

The Gamut

The high school students had mixed opinions on the issue of prayers ranging from "nice" to a neutral "it wouldn't hurt" to strong objections. One group of students had planned to boycott Friday's homeroom period to protest the law, but one of the organizers said only about 40 students joined the effort.

The School Committee at its March 4 meeting directed Superintendent of Schools William C. Lannon to draw up guidelines for implementing the prayer law. The guideliness include:

* The homeroom teacher must announce a student's right to volunteer a prayer;

* Other students must respect the rights of students who wish to pray by remaining quiet;

* Non-participating students and teachers may leave the classroom;

* The prayer may not be longer than a minute;

* A student may also request a moment of silence.

These provisions replaced a law which required the teacher of the day's first class to announce a moment of silence.

Until two weeks ago, the school committees of Cambridge, Newton, Brookline, and Beverly had decided not to comply with the prayer law. At a February 5th meeting the Cambridge committee decided to delay making a decision on whether to comply with the law, ignoring the February 5th effective date of the law pending the results of litigation.

The Massachusetts Civil Liberties Union and a group of parents from Marblehead and Framingham are currently challenging the constitutionality of the new law.