He didn't trust the word of Hitler. He simply thought that Hitler was too weak to conquer the Soviet Union (and it of course turned out that he was) and that he was much stronger than him (after all the Germans had 3150 tanks, that were at that time nowhere as good as T-34 and KV's, and the Soviets had ca. 21000 tanks, including ca. 2000 KV's that were practically immune to any German attack, plus the Soviets had 3 times as many planes). Because he considered Hitler to be a reasonable guy he didn't think that he would risk a war with the USSR in a situation in which he was already at war with UK, and had a very realistic chance of engaging USA into it. By the way he of course himself planned an invasion on Germany. At the beginning the Soviets were supposed to invade on 6th July 1941 but then the invasion was postponed until 1942.
Hitler was NOT too weak to conquer the Soviet Union. Hitler just did some heavy miscalculations, one of which was to assume that Stalin wouldn't send millions as cannon fodder in Stalingrad; and he he had too huge an ego to let his generals handle the operation. Hitler was very smart as far as managing lower level combat, but he knew little about total army movements and macrostrategy.
Hitler had no plan of engaging the USA into it. Hell, he didn't even want to engage Britain in it. Britain engaged in it herself in defense of Poland. Hitler had always dreamt of an alliance with Britain (read about Ribbentropp's activities in England and read Mein Kampf) and didn't care much about overseas colonies, accepting the British empire as part of global culture.
I would love to see some evidence that Hitler wanted to drag the USA into a war. Sounds very far fetched to me.
And this is coming from a Sephardi Jew, not a Nazi apologist.
The French and British were also stronger, but that didn't save them. Hitler made the fatal mistake of settling for economic goals in the Ukraine in August of 1941, rather than directing an attack on Moscow from Smolensk to finish off the Soviet State apparatus in the original campaign timetable of 3 months, and only then turning south to create a line of control from Arkangelsk to Astrakhan. Moscow was the nerve center of Soviet telephony, railroads, roads (such as they were) and other means of communication and control. A rump Soviet state might have survived beyond the Urals after this fall of Moscow, but it would have had little power without the manpower of the Russian heartland.