for what little it's worth, below is post that I sent the other day but which must be floating somewhere in cyberspace...
Boyhood friend of mine's father was one of cryptographers who intercepted/decoded Japanese messages as early as Nov. 27. As I recall story he told (almost 40 years ago now), US had info indicating likely attack but thought Philippines would be target.
I've since read that US decoded message by Dec. 6 revealing Japanese attempt to get info about US ships at Pearl Harbor and that neither an adequate attempt to check local security nor adequate warning to local commanders was issued.
But Secretary of State Cordell Hull was expecting attack somewhere prior to interception of any messages given that he mentioned it during three separate Cabinet meetings in Nov. (see Herbert Feis' favorable account of US behavior/policy in his book _The Road to Pearl Harbor_).
Prior US-Japan negotiations were destined to fail because former refused to drop demand that latter accept 'free trade' that no countries, including US, practiced at time. Paul Schroeder (_The Axis Alliance and Japanese-American Relations, 1941: An Appraisal of the American Policy_) documented both Japanese diplomatic attempts to avoid war via concessions on China (contrary to official US account) *and* trade discrimination that US and other countries practiced against Japan.
Charles Beard argued in _President Roosevelt and the Coming of War, 1941_ that US goaded Japanese in order to enter war in Europe. Mainstream historians (Schroeder, liberal Schlesinger, conservative Ambrose, among them) have disputed this, but fact of matter is that racist anti-Japanese sentiment was higher in US than were anti-fascist views before Pearl Harbor. And US manipulated racist sentiment (interning over 100,000 Japanese-Americans in process) following Pearl Harbor even as it prepared to focus upon European theater.
Re. Roosevelt, New Deal had been intellectually and politically dried up for several years, his desire to enter war on side of British was well- known, and gradual escalation of embargo against Japan over two year period forced Japanese to take offensive in Asia in search of alternative sources of fuel and raw materials. US would have pursued whatever policies - diplomatic, military, or otherwise - deemed necessary to settle differences in favor of its imperial interests. Michael Hoover