are target-local variables for pattern rules well defined and supported?

[Britton Kerin]

This seems to work:

%.o: COMPILE = cp
%.o: %.c
         $(COMPILE) $< $@

but it makes me a little nervous.  The manual doesn't seem to mention
it in either the section on target-local variables or the one on
pattern rules.  Is this well defined and intentionally supported
behavior?

Thanks,
Britton