I have a broken air conditioner that plugs into my 220V USA wall
socket. Its prongs look quite different from typical 120V appliance
prongs. Before next summer I'd like to buy a 120V portable room air
conditioner. Is there a converter available that would allow me to
safely plug the 120V 3-prong socket portable air conditioner into
the 220V outlet? Thanks.


By "portable" A/C do you mean free-standing, or a window-mounted, unit ?
how many BTUs are you looking for ?

Free-standing, like this 115v/12,000 BTU unit from Amazon:
https://urlzs.com/TXnw9

Is there no standard 120 volt outlet nearby ? Even if a heavy duty
extension cord is needed ?

I'll use that if I have to but the unused 220v socket is on its own
circuit. No extension cord needed.