A federal grand jury in North Carolina is currently investigating possible civil-rights violations in the slayings of five social activists by Ku Klux Klan and Nazi party members in Greensboro in late 1979. Relevant testimony which did not come out in a 1980 trial -- six klansmen and Nazis were acquitted of murder charges -- has been presented to the grand jury.

What was initially perceived of as a group of right-wing low-lifes firing in claimed self-defense against some social activists with unpopular political views is now a case that raises questions of possible collusion -- before and after the killings -- between government officials and the hate groups.

The case has national importance. The Klan has become brazen in the last couple of years. This past week several rallies were held in Connecticut. This brazenness coincides with increasing public pressure on the Justice Department to prosecute civil-rights cases.

What is being called the Greensboro Massacre occurred shortly before noon on Nov. 3, 1979. A group of some 100 demonstrators had met to begin a legally sanctioned march in a Greensboro black neighborhood that was to end nearby in an anti-Klan conference. A caravan of klansmen and Nazis, in vehicles carrying about 40 members of the two groups, appeared on the scene.

Words were exchanged. Within minutes, some of the Klan-Nazi group were shooting into the crowd. Four demonstrators died there. One succumbed two days later in a hospital.

The victims included: two young physicians, one of whom was also president of the Amalgamated Clothing and Textile Workers Union chapter at a North Carolina factory; a master's degree graduate from Harvard Divinity School; a Duke University honors graduate who worked at the school's medical center; and a union organizer at a textile mill.

Last April, two television cameramen who had filmed the shootings said they told the grand jury that the gunplay appeared to be a well-planned attack. Two months ago, an ex-Nazi said he testified before the the grand jury that an agent of the federal Bureau of Alcohol, Tobacco and Firearms, who had infiltrated the Nazis, asked him to hide suspects after the shootings. And last month, the grand jury heard from a former klansman, who is also a former FBI informant and recently a paid Greensboro police informant, who led the caravan to the scene.This informant told the press that Greensboro police knew the time and place of the march, and that the Klan-Nazi caravan would be on hand. But the police did not appear, neither to warn the demonstrators of a possible attack from the gun-laden caravan nor to prevent members of the Klan-Nazi group from drawing weapons.

In the state trial that acquitted the six accused of being the gunmen, the police informant was not called to testify. Nor was the BATF agent.

On the day of the shootings, four of the victims were members of the Communist Workers Party, a relatively new group in American politics. A month before, they had been calling themselves the Workers Viewpoint Organization. Whatever their banner, in practice their radicalism wasn't much different from the kind that prompts scores of educated and motivated social activists -- from VISTA volunteers to Catholic sisters -- to assist the poor throughout the South.

The case of the slain Greensboro Five is reminiscent of the Wilmington Ten and the Charlotte Three cases in the 1970s. Then, as now, questions persisted about the reliability of witnesses, the fairness of jury selection, and the reluctance of federal officials to probe deeply.

Another striking similarity is that national groups and leaders are again rallying to demand that questions and suspicions be dealt with by federal authorities -- or, as the Greensboro Justice Fund is asking, by an independent special prosecutor. The groups and individuals include the National Council of Churches, the American Civil Liberties Union, the Christic Institute in Washington, several members of the Congressional Black Caucus, the Peace and Justice Ministry of the diocese of Raleigh, and Catholic bishops Walter Sullivan and Thomas Gumbleton.

At some point, a congressional oversight committee might have to involve itself. As the Klan and other reactionary hate groups grow bolder, in Greensboro and elsewhere, then Congress and the public need to know whether federal agencies are becoming bolder about stopping them. It isn't a passing issue, nor is it peculiar to the South.