WHEN SOMEONE WHO has done as much as Vernon E. Jordan Jr. to improve the lot of black Americans is shot in the back, it is obviously a major public happening. When facts are few for more than two days after the incident, the very absence of details feeds all kinds of potentially harmful speculation, from rumors on the streets to ill-considered statements of reaction by public figures.

While people everywhere have been pulling for Mr. Jordan's complete recovery, they also have been understandably anxious to find out exactly what circumstances -- racial, political, personal or otherwise -- led to the shooting of the president of the National Urban League. This is why the swift entry of federal investigators into the case was so critical. Every available law enforcement assistance should be extended to the state and local authorities in Indiana. Already, the sensitive nature of this job has been evidenced in the different initial characterizations of the case by local officials and the FBI.

Some of the statements emanating from the national level, we have to add, have been especially unfortunate. Only hours after the shooting and without furnishing any supporting evidence, President Carter flatly and unwisely labeled it an "assassination attempt." Sen. Edward Kennedy called it "another reminder of the senseless violence that stalks our land." The Rev. Jesse Jackson expressed his belief that there is "some kind of hit list" that threatens the black leadership, though he was quick to add his hope that "the brothers and sisters would not panic. It would serve no useful purpose."

It certainly wouldn't. There is no reason to doubt that the FBI and other authorities are vigorously pursuing all angles.Until more is known and reported, open-minded patience is all the more a virtue.