The President's Daily Brief (PDB), a highly classified intelligence report prepared daily for the President of the United States,"is the quintessential predecisional, deliberative document," the Central Intelligence Agency argued recently in court, claiming that virtually nothing about it can be made public even after several decades have passed.

But a 1970 memorandum disclosed this week at the Nixon Library sets aside any such reticence and provides a detailed look at the preparation, evaluation and reception of the PDB.

Meredith Fuchs of the National Security Archive, who litigated a Freedom of Information Act case earlier this year seeking access to historical PDBs, expressed surprise at the new release.

"What is most amazing is that one day they say the method of producing [the PDB] is so secret that nothing about the document can be disclosed, and then not long after they release this detailed, hour by hour explanation of how it is produced," she said.

The 1970 memorandum, written by Andrew Marshall for Henry Kissinger, describes strengths and weaknesses in the PDB process, and proposals for improvement.

But the biggest"secret" about the Daily Brief may be what Marshall described as"the widely shared suspicion that the President does not ever read the CIA PDBs."

As for the selection process that determines what to include in the PDB, Mr. Marshall wrote in his Top Secret Codeword report,"It is derived... to a large extent, I believe, from a sense of what's timely as judged from the New York Times, press, and wire service coverage."