New Hampshire State Police officers arrested 42 members of the Boston Clamshell Alliance Saturday on charges of criminal trespassing as they entered the construction site of the nuclear power plant at Seabrook, N.H.

The police released 21 members of the group shortly after their arrest on $100 bail. The rest of the demonstrators remained in jail to call a hunger strike and demand release on personal recognizance.

Deborah Givner, a student at the School of Education, and Victor Manfredi, a graduate student in linguistics, remain in jail. Both are on leave from Harvard.

Demonstrators climbed over the site's fence at two places at 7 a.m. Saturday. State troopers arrested them for trespassing, preventing them from their stated purpose of interfering with the construction project.

At 1 p.m., a separate wave of Clamshell demonstrators vaulted a fence onto power company property in order to protest the blocking of a local road by the power company's fence. The police also immediately arrested the demonstrators.

A spokesman at Clamshell's Portsmouth, N.H. branch yesterday cited the "doctrine of competing harms" as the major legal issues in the two incidents. The Clamshell group said the danger posed by the presence of the plant overshadows the danger posed by the demonstrator's act of trespassing.

Three of the jailed demonstrators said in a statement they are "eager to face the courts" and added they were jailed for "political convictions and not criminal activities."

New Hampshire State Police spokesmen were not available yesterday for comment.