key switch rated 220v 1A is it OK to use 12v 3A
The voltage and current ratings of a switch shouldn't be equated to power. Instead, both are separate limits to what the switch is rated to handle.

Exceeding the max voltage (even without current flow) may result in internal arcing and/or short circuits.  Exceeding the max current (even at a low voltage) may result in the switch conductors getting hot and melting, and perhaps welding together.

So, what you need is a key switch that can handle (at least) 3A, and also (at least) 12V.

When looking for a DC-rated component, there is another complexity: DC is more difficult to switch than AC, so the switch may have a much lower rating for DC.  When you're looking at datasheets make sure that it is rated for 3A DC, not just 3A AC.