As federal security officers looked on calmly, demonstrators yesterday afternoon built a small barricade of pine trees on the steps of the Central Square post office to protest the second day of the renewed draft registration program.

Unlike Monday's demonstration in a downtown Boston federal building, which resulted in 22 arrests and several incidents of security officers beating or wrestling with protesters, yesterday's rally ended without arrests or attacks by federal guards.

Demonstrators did not prevent people from entering the post office, but they did advise 18-year-olds going in to register that not signing up would "prevent the draft and the war that is coming."

The only fighting broke out when two young, male pedestrians argued with and then assaulted several of the picketers in two unrelated incidents. Cambridge police removed one man for his own safety, after he twice attacked a member of the Marxist-Leninist Party who was carrying a sign mocking President-elect Ronald Reagan. Police said the man would not be arrested.

Demonstrators arrested during Monday's protest yesterday accused officers assigned to the McCormack Federal Building in Boston of unnecessarily clubbing a juvenile taken into custody, causing him to bleed from the head. A spokesman for the U.S. Attorney's office in Boston acknowledged yesterday that there had been several allegations of illegal police brutality but refused to comment on them.

Led by several members of Veterans Against Foreign Wars, 35 demonstrators, some carrying placards and chanting antiwar slogans, assembled by 11 a.m. in front of the post office. They were later joined by others who dragged small pine trees down Inman Street, across Massachusetts Avenue, and up onto the post office steps.

Initially, some of the demonstrators struggled with the 15 officers and postal inspectors, who stood at the top of the steps, over the placement of the trees, some of which still had Christmas tinsel hanging from their branches.

But the officers then helped the protesters pile the trees in a neat four-foot barricade, leaving a passageway for pedestrians to enter and leave the building. Few of the demonstrators, most of who were over registration age, entered the post office, and the barricade was removed late in the afternoon.

Xmas Power

"The Christmas trees show the militarists that there is something better than violence, that we don't want registration," Heidi Davis, one of the demonstrators, said after leading a mock nuclear annihilation scene, in which protesters dropped to the ground and screamed.

Davis, whose face was smeared with tomato soup to simulate a head injury, added, however, "I guess we really haven't succeeded, because people are still registering."

A post-office clerk estimated that 25 men had registered by midday.

Other demonstrators, many of them members of the Boston Alliance Against Registration and the Draft (BAARD), described the protest as a success for drawing media attention and reminding six people that anti-registration sentiment still exists.

Few students from Harvard, however, have participated in this week's anti-registration efforts, Hilda Marshall, a member of the Radcliffe-Harvard Peace Alliance (RHPA), said, adding, "Most of (the RHPA members) are in the library studying."

"People at Harvard are definitely against registration; they just have not come out," Marshall said. Several protesters said sub-freezing temperatures have kept picket lines short.