For an afternoon in a D.C. community center yesterday, an eclectic group of activists hunkered down to the nitty-gritty of protest -- training for the planned nonviolent "blockade" this morning of the White House's Pennsylvania Avenue entryways.

The tight focus on how to get arrested in a peaceful act of civil disobedience belied the diversity of a group composed of teen-aged students, old hands from the antiwar movement, a Gray Panther and veterans of protests in Chile and West Germany.

They were among thousands demonstrating in Washington this weekend under a banner of many different causes: opposition to U.S. military intervention in Central America; support for job creation, military budget cuts and a nuclear freeze, and opposition to U.S. and corporate support for South African apartheid. The weekend's activities were organized by a coalition calling itself April Actions for Peace, Jobs and Justice.

At the nonviolence training session where about 200 dissidents were broken into six groups; one man asserted that a newly strengthened protest movement is afoot. "After the reelection of Reagan, people are willing to do something extra," said Frank Panoupolos, a leader of one nonviolence workshop.

Michael Wenberg, 32, of Minneapolis, said he observes a lack of cohesion among dissident interest groups, however, and a "mushing of the issues."

And Yvonne Logan, a 67-year-old leader of the Women's International League for Peace and Freedom, complained that groups aligned against the Reagan administration are numerous but are short on strategy.

"All the people who support the nuclear freeze don't know what to do anymore," she said. "And our Congress doesn't seem to react. Reagan has got everybody bamboozled."

The disparate views of protest in America did not interfere with preparations for today's "action." Leaders of April Actions expect about 300 people to meet at the Lincoln Memorial at 7:30 a.m. and walk to the White House, where "affinity groups" of 15 to 20 protesters each will stage the event.

"Our plan is for a few affinity groups to block the entrances, while others will spread themselves out along the sidewalk," an April Actions leaflet says. "If the police clear people out of the entrances, others will move in to take their place. If nothing exciting has happened by 11:00, we may decide to shift our tactics, moving into the street or around the corner. We will not attempt to cross the fence and enter the White House grounds."

Participants in the workshops heard a brief resume of civil disobedience in the United States, volunteered their fears about arrest, listened to a description of arrest procedures in the District and engaged in role-playing scenarios designed to simulate protest conditions.

Frank Collins, a 67-year-old Gray Panther from this area, commented on Saturday's rally at the Capitol: "Yesterday's was the best demonstration I've seen in a long time . . . . It was just great to see the gathering of people after a 10-year lag when we were basically between shows."

Francisco Bisquertt, a 24-year-old American-born man who was raised in Chile, told the group he was not worried about the arrest procedures in the District. In the authoritarian nation of Chile, he said, it is not so easy to protest.

"What they Americans forget is that they are allowed to protest here," said Bisquertt, a member of the Humanist Party. " . . . In Chile it is hard to get anybody to protest in street demonstrations because they get arrested -- not for a day, but for a week at least."

Stig Palm, a 20-year-old Swede attending Bates College in Maine, said he has had a hard time finding any companions in dissidence on campus. "I think they [classmates] are interested in other things," he said. "I think they are very conservative. In that college, I don't know many people who support me."

Still, Palm believes it is important to speak out while he is in this country.

"I can make whatever statement I want in Sweden, but I doubt it can make any difference . . . . If I can make a statement here it goes to Reagan directly."