NEW YORK (AP) _ Vandals ransacked classrooms and set two fires at a Jewish school during the weekend and a spokesman for a Jewish activist group said today its members would patrol the school with shotguns and baseball bats.

Rabbi Yakov Lloyd said members of the Jewish Defense Group would set up security around the Talmud Torah Toldos Yakov Yosef Yeshiva in Brooklyn$

Police Sgt. Frederick Lewis said department policy discourages such action by civilians and warned that police would intervene if guns were used.

''If people have shotguns in a car or on their person, they're going to get locked up for weapons charges. That's it,'' he said.

Police said officials at the yeshiva had discounted anti-Semitism as a motive in the weekend burglary, the second in two weeks at the school.

However, Lloyd, who is not attached to the school, said he believed the incident was deliberately anti-Semitic. His Jewish Defense Group is a splinter group of the extremist Jewish Defense League.

Vandals broke into the yeshiva sometime between 7 p.m. Saturday and 7:30 a.m. Sunday, possibly by breaking through a window on the roof, said police Sgt. Diane Kubler. She said it was not clear if anything was stolen.

The vandals set fires in the ark and in the dining hall. The blazes were extinguished by the school's sprinkler system, causing an estimated $30,000 in water damage, police said.

Lloyd said about 15 members of the Jewish Defense Group would patrol the yeshiva.

He said two members of the group who have licenses for shotguns would carry them. ''Others will carry baseball bats,'' he added.

He said he did not ask the school for their approval.

A phone call to the school for comment early today went unanswered.

Two weekends ago, thieves stole a copying machine, a video projector and small valuables from the school, said Simon Weiss, who answered phones at the yeshiva Sunday.