No violence broke out when a gathering of 24 robed Ku Klux Klan members stood in a suburban park here the other day to gawk at each other and bear crude witness to the cult of bigotry. Nearly 300 policemen, more than 12 times the number of Klansmen, were on hand to ensure that the group's First Amendment rights would be protected.

Only three weeks before, police in Boston were less successful in letting racism have its say. When 23 Klan marchers on their way to a downtown plaza for a rally were the object of minor disorderliness from a few protesters in an assembly of 1,000, the police stormed the crowd. Citizens told of being clubbed and Maced. Charges of police brutality were made, with the police denying them.

It is tempting to dwell only on the theatrics that accompanied the recent stirrings of the Klan. The rawness of their hate invites easy denunciations. And shortly, if plans are carried out for the organization to march down Pennsylvania Avenue for a rally across from the White House, the Klan will have a national audience. Most of the country will have no trouble being sickened by the Klan's latest display.

Well beyond the emotionalism of the marches and counter-marches is another, less visible, aspect of Klan violence that raises questions not only about the group's audacity but also the legal system that ought to control it.

At the moment, the Justice Department is involved in an exchange with the Greensboro Civil Rights Fund, a group seeking to establish responsibility for the killings of five social activists in Greensboro on Nov. 3, 1979. A group of six Klansmen and Nazi party members was acquitted by a jury in 1980, but since then, testimony has been given to a grand jury that suggests the original trial was flawed.

Parallel to the grand jury's deliberations is the issue of whether or not a special prosecutor is needed in the case. Lawyers for the widows and families of the slain activists (who were members of the Communist Workers Party) have argued persuasively that the need is strong. The lawyers allege that both the FBI and the Bureau of Alcohol, Tobacco and Firearms were involved in planning and executing some of the actions that led to the killings.

In an effort to get an impartial eye to look at the case, the Greensboro Civil Rights Fund filed a motion on Sept. 23 in U.S. District Court here. The court, which has jurisdiction in this matter, notified the Justice Department through a summons that it had 60 days to respond to the court motion filed by the Fund.

But on Oct. 1, D. Lowell Jensen, assistant attorney general for the Criminal Division, wrote to the Fund saying that the Fund's allegations of government involvement were not sufficiently specific to move the department to act. The press was notified of this letter before it reached the Fund's lawyers, and news stories ran on Oct. 5 saying that no special prosecutor was being appointed.

The stories did not say that Jensen's decision was premature and that his letter was a tricky end run. In fact, the department was -- and still is -- in the 60-day period of working up a response to the summons from the court. Last week, a Justice spokesman said the department has made no effort to correct the misperception it created.

Although the Reagan Justice Department appears to be unconvinced that a special prosecutor is needed in this case, the Fund's allegations were specific enough to persuade nearly a thousand black North Carolinians and several hundred national civic leaders, including members of Congress, that the government cannot be trusted to investigate charges against itself.

The intricacies of the Ethics in Government Act, which contains the special prosecutor provisions, are far removed from the foul noisiness of the Ku Klux Klan. But five citizens are dead, and their killings have not yet been explained. Little of the wrath that is justifiably vented against the Klan as it stages rallies across the country appears to be drifting upward to the high officials entrusted with decisions about solving the Greensboro killings.

The Justice Department appears to be more intent on making the case that the Greensboro Civil Rights Fund is a pest group of legal upstarts. It is not. It understands the Klan all too well. The more these violent racists are coddled, the bolder they become in the streets.