It wouldn't have been as easy as simply telling them not to do it. Roosevelt actively desired the war by completely destroying Japan's access to Western resources for its industrial economy in the years prior to the attack. Not to mention, the U.S was already prepared to fire the first shots of the war before the attack happened, considering the fact that the USS Ward sunk a Japanese midget submarine approaching Pearl Harbor an hour before the planes began bombing, killing two Japs, yet with little additional security precautions taken in the hour following that fatal incident.
I believe it was very likely that Roosevelt and the U.S government had foreknowledge that Hawaii would've been an imminent target, and, had the Japs held off, I also believe that the Americans would have done more conniving just to eventually generate the conflict.
