AGAIN -- AS WE did last July, again in August and then in December -- we raise an increasingly important question about the duration of a grand jury investigation and whatever relationship it may have to Mayor Barry. Because there are still no facts known by the public, the question remains: How long does a mayor, a city administration and everybody who lives here have to stay under this cloud?

We put the question to U.S. Attorney Joseph diGenova again on Thursday. As on previous occasions, he cited a commitment to keep the proceedings confidential, which is entirely proper -- even though there were leaks and rumors last summer that had to have come from some informed authorities.

Mr. diGenova insists that he shares the public concern and recognizes the special need for "expedition when public officials are involved." The matter is "being handled expeditiously," Mr. diGenova argues, adding that "it is important for us, too, to resolve this as quickly as possible. That has to be our paramount interest."

That remains to be seen. Just as there is no official public evidence on which to make any assumptions about those under any grand jury investigation, Mr. diGenova's conduct of the investigation has yet to be fully assessed. We do note, though, that this jury's term is due to expire in about a month and a half; at that point -- if not earlier -- the authorities will owe the public either an announcement of the end of the grand jury's work or an explanation of why the jury's term should be extended. The sooner the better.