UNITED STATES starts the war as a neutral major power. She may not join or be attacked by the Axis.
The USA may start building the British Lend-Lease Convoy [B] in 1941.
7.71 Lend-Lease Convoys: convoys [A]
and [B] are built by the USA and require USA resources. These convoys are actual PP for the Soviets [A] or Britain [B] as if they were factories. Convoy [A] cannot be built until the USA and. Convoy [B] can be built starting 1941 even if the USA is not at war. Attacking this convoy is not a DoW.
Given the above, can US naval units escort LL Convoy B before the US is at war? It would seem not, as if the Axis can not attack, it can not take losses, and as not at war the escorts can not in turn fire back.
OTOH, it might be that the presence of a single US naval step with the convoy makes it immune to attack.
It is notable that the US is not covered by a rule similar to the one for Italy:
While neutral, Italian and Allied navies can move through each other, but cannot stop in the same zones.
Which implies that US and Axis units can co-locate, which tracks with the Axis being able to attack Convoy B without it being a DOW.