More than two dozen demonstrators, among them a third Berrigan brother, were arrested at the Pentagon yesterday morning after attempting to block entrances and smearing the building's walls with what they said was human blood.

About 150 demonstrators began gathering at 7:30 a.m. on the parade grounds outside the Pentagon's river entrance in the second day of anti-nuclear arms protests. The event, sponsored by the Atlantic Life Community, began Tuesday with a peaceful encirclement of the military complex by 250 persons carrying signs and balloons.

Yesterday, about 15 persons were carried away by police when they tried to block the Pentagon's mall entrance. Another five persons, two of whom were identified as priests, were taken into custody after they chained themselves together at a tunnel entrance to the building.

Gerald Berrigan, a schoolteacher from Syracuse, N.Y., who is a brother of activists Daniel and Philip Berrigan, and seven other persons were arrested after they splattered a red liquid on four pillars beneath the offices of Defense Secretary Harold Brown.

Of those arrested, 27 were taken to Alexandria for arraignment before a federal magistrate. Five who agreed to immediate trials were sentenced to 10- to 30-day jail terms and taken to Richmond because of overcrowding in Washington-area detention facilities. Berrigan, ordered held under $1,000 bond, was placed along with seven others in the D.C. jail. Eleven were transferred to Arlington. Three were released on bail, and four other persons were issued citations to appear later in court.

About 50 demonstrators remained outside the river entrance, some of them seated, arms linked, on the building's steps while others sang songs of the peace movement. Most employes entering the building, including military personnel bearing food for New Year's Eve parties, walked around them.