I definitely would not say before 1940 and would have to mark the beginning of 1941 as the point that any joint British/American planning took hold.
I mean, obviously there is a history on the possibility of war between Japan and the U.S. dating back to the end of World War I and Japan's endowment of the German possessions in the Pacific. These islands in the Marshall's lay in between the commerce routes for the U.S. and it's Philippine possession, and of course Guam was stuck right in the middle of it all. Ergo we have the Orange Plans which will continue to evolve during the 20s and 30s and will be ignored by MacArthur exasperating the situation on the Philippines come the end of 1941 (and for which he should have been relieved of command).
But at the same time, Orange Plans had no bearing on any joint American/British policy. In fact quite the opposite. Even into the late 30s there were variations of an Orange-Red Plan which planned around the possibility that the United States would be at war with Britain and Japan at the same time. It was not until Britain was at war with the Nazis that War Plan Red (war with Britain) and its derivatives were finally put to bed and the United States gravitated to the British cause against the Axis.
The United States had already begun looking at the Axis problem before this with the commission of the Rainbow Plans in April 1939 but this was independent from any planning with the British. In fact, of the first four Rainbow plans, only one of them, Rainbow 4, had Britain listed as an ally to the American cause. Rainbow 4 called for full support of Britain and France against Germany and Italy. With this plan it would also suggest that America cover the Pacific since it was assumed that the British and French could cover the Atlantic. A derivative of Rainbow 4 was developed later and designated Rainbow 2. Rainbow 2 called for America to concentrate its offensive activities to the Pacific while Rainbow 4 (Now called Rainbow 5 with the insertion of the new Rainbow 2) called for a defensive posture in the Pacific while resources were dedicated to the defeat of Germany/Italy. This was the final plan that was accepted by early 1941.
Before that though, the Joint Board and the Joint Planning Committee focused their efforts on Rainbow 1 which called for the unilateral defense of North America above 10 degrees north latitude.
After the fall of France, in June 1940, there was zero possibility that Britain alone could defeat Hitler, while America took care of Japan in the Pacific.
Therefore, all US planning was focused on first defeating Hitler, only then going after Japan.
And I'm hoping I won't have to go digging through books to find references for that... ;-)
But the main point here, in response to beebuster2000's original comments is: from the very beginning (whenever that was), US planners saw the war as another World War, that must be fought victoriously all over the globe.
At no point (that we know of) did President Roosevelt ever contemplate giving Japan everything it wanted so as to avoid war entirely in the Pacific.
Indeed, whether the Pacific was to be the major theater of war, or just an after-thought, may have changed with the fortunes of war in Europe, but at no time did the US seriously plan to buy peace with Japan in order focus on defeating Hitler.
Of course, had Hitler knocked Russia out of the war, that may well have changed things.
But as it turned out, the US always intended a two-front war.