Of all the forces (overt and covert) at work in troubled Central America, one of the least-publicized is Peace Brigades International (PBI). This unofficial organization, which traces its roots to a concept Mohandas K. Gandhi voiced in 1922, has established in the past year what its leaders call ''a presence'' in Guatemala. Its aim is ''to help protect the people of Central America from the violence that is destroying them, and to stand by them as they work to create legitimate political channels of change.''
Daniel Clark, a lawyer from Walla Walla, Wash., and international secretary of PBI, explained recently PBI's current role in Central America. It began in May 1982, when an international team visited Costa Rica, El Salvador, Honduras, and Nicaragua to study border and refugee problems.
Another team was sent to the region in January and spent two months visiting conflict areas and ''exploring the need for peacemaking.'' In March, Mr. Clark says, PBI decided to put the team in Guatemala to monitor the first month of then-President Efrain Rios Montt's announced ''political opening.''
Brig. Gen. Oscar Mejia Victores, who took power in a coup last week, has vowed to legalize political parties and hold elections in Guatamala next year. Observers are watching to see if General Mejia Victores moves more quickly toward reform than Mr. Rios Montt, who made similar promises when he assumed power in March 1982.
PBI now is in the process of expanding the team to five members from five different nations to serve in Guatemala for a year, Clark says.
''It is too early to say what the character of the new regime will be, but we expect our work to be continuing,'' says Clark.
PBI team members also observe and report on human rights conditions. At the same time, Clark points out, they must not only carefully maintain neutrality in terms of national politics, but also in relation to contending local groups. Otherwise, he explains, the PBI team not only would probably be asked to leave the country, but it would be unable to perform what may be its most useful service - ''opening channels of communication between groups.''
Many Guatemalans, says Jo Leigh Commandant of Toronto, coordinator of Central American projects, are isolated by poverty, illiteracy, racial and language barriers, and lack of contact with the outside world. Even when help in tackling problems is available, she says, they are unaware of it. PBI workers try to help these people become better informed. PBI also believes, says Ms. Commandant, that it can help resolve or avoid class, cultural, political, religious, and other conflicts by acting as a go-between.
So far, according to Clark and others who have been in Guatemala, the PBI effort is mostly in the ''trust building'' stage.
Unlike the US Peace Corps or UN volunteers, PBI members usually do not provide ''services'' such as teaching. They seek to ''serve the civil peace of a society'' and encourage nonviolent change - clearly walking a thin tightrope politically.
PBI was founded in September 1981. According to the founding statement, ''If hostile clashes occur, a brigade may establish and monitor a cease-fire, offer mediatory services, or carry on works of reconstruction and reconciliation.''
Gandhi envisioned peace brigades as helping reconcile differences between Hindus and Muslims after Indian independence, says Charles C. Walker, a PBI cofounder and former member of the World Peace Brigade, which formed in 1961 but lapsed after several years. Shanti Sena (Peace Brigade in Hindi) was founded after Gandhi's assassination and still functions in India.
Mr. Walker, author of ''A World Peace Guard: An Unarmed Agency for Peacekeeping,'' is general coordinator for PBI. He cites a number of precedents for the organization's activities, including the World Peace Brigade's participation in the Zambian independence effort and Shanti Sena activity in response to conditions in East Pakistan (now Bangladesh).
However, PBI leaders say, most of those activities involved direct services and sometimes political commitment. PBI seeks to pursue nonpartisan peacekeeping.
Supported by private contributions, PBI is trying to raise $15,000 for the initial phase of its Central American project.