First US atomic bombs were tested in 1945. Pearl Harbor was in 1941. That's a no.

So youve gotten the obvious correction that the bomb, and even serious work towards a bomb would not begin until after the attacks on Pearl Harbor and elsewhere in the Pacific to open the war.

But OP I gotta ask where you heard or got the idea that the US had atomic bombs before its entry into WW2.

If there is some source or place spouting that sort of wildly inaccurate information with even a veneer of credibility then they need to be flagged and hopefully corrected.