About 80 animal-rights activists, fortified by potato chips, pretzels and grape juice delivered in dramatic fashion, settled in for another night yesterday at National Institutes of Health offices they have occupied since Monday morning to protest brain experiments on monkeys.

The demonstrators said they have no plans to leave unless police arrest them or NIH agrees to halt funding for brain-trauma experiments at a University of Pennsylvania primate center. An NIH spokesman said there are still no plans to arrest the protesters or meet their demands.

For several hours yesterday, police refused to let grocery bags filled with food and fruit juices be taken to the eighth-floor offices occupied by the group. They relented only after demonstrators were able to hoist a box of food up to an office window by rope.

The People for the Ethical Treatment of Animals, which organized the protest, took over the office of Dr. Murray Goldstein, director of the National Institute of Neurological and Communicative Disorders and Stroke, about 9 a.m. Monday.

The demonstrators originally demanded an end to NIH funding for research at the University of Pennsylvania Head and Injury Laboratory, but Monday night they modified the demand, instead asking for a halt to funding until an NIH review of the research is evaluated. Dr. William Raub, NIH department director for outside research, termed that demand "nonnegotiable."

Yesterday, Alex Pacheco, the group's leader, and attorneys for the group met for a second time with Goldstein and Raub.

Neither doctor would comment on the meeting, but Pacheco said no progress was made during the hour-long discussion.

About a half-dozen protesters, including the youngest and oldest, left for home yesterday morning. They were replaced by other protesters who blocked the front doors to the adminstration building. Group members said they had hoped the action would prompt arrests by police.

Patricia Freeman, 67, of Claymont, Del., said she had to return home to feed her dog and cat, while Claudia Gitman, 16, left with her mother for their farm in Pottsville, Pa., disappointed because they had not been arrested.