There are many things we know about the Attack on Pearl Harbor.  It was only a raid. No plans were ever made to actually invade the islands. (Combat Command, Fredrick C Sherman, Dutton, 1950)  Had the force been sighted two days prior to the attack, the whole thing would have been called off.  This would have left us to wait for the attack on the Philippines before we would have been at war. ( The Pacific War 1941-1945 , John Costello, Atlantic Communications Inc., 1981)

       A large amount of Japanese activity was happening all over the South Pacific. We were aware of much of this movement, although not in total detail.  British interests were also the target of the Japanese movements.  We were breaking the English codes as well as the German, Italian and Japanese codes.  Because of the constraints placed on us under the Neutrality Act and because we were afraid of the Axis changing it's code system, the number of people to actually be involve in code breaking was fairly small.  As the actual start of operations against us neared, the volume of work increased.  This necessitated some messages being "passed over" as less important. This was an error. Another error was the belief that only the most "Important" information should be shared with  The president and his staff.  More information was kept from the Navy at Pearl.   From 1940 on, repeated WAR Warnings were sent to the Hawaii Islands and other parts of the Pacific. Like the Boy calling, "Wolf!" These warnings became routine and were disregarded as unimportant.
    There remain at least two unanswered questions. Although they  would not change the course of the War, they are interesting.
    Did England know about the attack?  Some of the documents dealing with British code breaking around December 7, were sealed for 75 years, an unusual amount of time.  Even if England did know of Operation Z, would she have any real compulsion to tell America of it's existence. America was Neutral at least in word.  England was at war and was expecting to be attacked by the Japanese at any time.  It is very possible that if the British knew anything about the attack they were too busy with their own troubles in the Atlantic, North Africa, the Med and the Pacific to spend much time worrying about keeping us Neutral.  Or it could have been that they withheld the information to insure our entry into the war on their side.  Either way, it would have made little difference.  We had enough warning from early 1940, on.  Our own Navy, in war games that year, had pulled the same raid off. We had the same information, the same technology, and were listening to the same codes, We can't hold the English responsible for something that was our responsibility.
    How much was known in Washington?  No doubt, the fact that we'd read the 14 part document that was to be delivered to Sec. State Hull at 1:00 tipped us to some Major event in the Pacific. Why did Hull keep the Ambassador waiting that sunday afternoon, after he arrived already half an hour late?  Could it be that our policy of letting Japan make the first attack including NOT letting them deliver a declaration of war before hand?  Even had the message been delivered on time, it would have taken time to evaluate, time we did not have.  Undoubtedly, the ability to proclaim a sneak attack united America as nothing else would have.

    I believe, based on the reading I've done, that Roosevelt was aware of an impending attack, but that he believed it would be launched against either the Philippines, or Malaya. (The British and Americans knew the movements of the Malayan attack fleet.) FDR knew the Philippines could (And did) hold out for months.

Airwar, Edward Jablonski, Doubleday and Company inc. 1971

Combat Command, Admiral Fredirck C. Sherman U.S.N. (Ret), Dutton, 1950

Getting us into war, Porter Sargent,, 1941

Japanese Warships of World War II, A.J.Watts, Ian Allen, 1966

Navy Air Colors-vol.1 1911-1945, Thomas E. Doll; Berkley R. Jackson; William A Riley, Squadron/Signal
     Publications, 1983

Peace and War, United States Foreign Policy 1931-1941, Government printing Office., 1942

The Pacific War 1941-1945, John Costello, Quill, 1982

The Wartime Journals of Charles A. Lindbergh, Lindbergh, HardCourt Brace Jovanovich inc., 1970

U.S Warships of World War II, Paul H. silverstone, Ian Allen, 1965

And various other sources