ABOUT 400,000 PIECES of paper go into the files of the Federal Bureau of Investigation every day and -- clearly -- sooner or later most should be destroyed. But the FBI should not decide which. Judge Harold H. Greene was right last week to order the National Archives and Records Service to work out with the FBI a new way to distinguish between dispensable documents and those that should be kept because of their historical or legal value.

The history of what has happened to those files over the last 40 years is not reassuring.The FBI told the archivist -- who has legal control over the destruction of government records -- what it wanted to destroy and routinely, almost automatically, received permission to do what it wanted. The temptation must have been great to keep the documents that made the FBI look good and eliminate those that made it look bad. It is remarkable, given the looseness of the arrangements, that so much actually does remain in writing about the darker chapters in the FBI's history.

Most of the pages that go into the bureau's files each day have no prospective value as history. Its investigations of stolen automobiles and most bank robberies, for instance, produce nothing that is useful to anyone after the needs of law enforcement have been met. These are files that can be destroyed once the FBI itself determines they have no further value. Keeping records merely for the sake of having them is a luxury that neither a Washington agency nor the taxpayers can afford. Government is not the Collier brothers.

But then there are the other FBI files. Its security investigations since the 1940s have probed the lives of famous Americans as well as millions of relatively unknown folk. Some of its criminal investigations -- from the pursuit of Al Capone through the Watergate cover-up -- document important incidents in the country's history.

It is in these areas that a professional historian's judgment about what should be saved is vital, in relation not only to the documents themselves but also to the way in which the information in them was collected. By halting the further destruction of FBI files until that judgment has been reached, Judge Greene has done history and orderly record-keeping a favor.