I've seen people argue just that on these boards. Years ago when I was just a lurker, but still....Perhaps in fact (though I doubt you would be able to come up with any rigorous distinction), but not in practice. Whoever launches a preemptive attack is by definition the one that started the war to everyone that matters. Nobody seriously argues that Israel didn't start the 6-day war, for instance, though what preceded it sure as hell wasn't peace.
If the Soviets launch a preemptive strike, then to the Western public, they will be the aggressors, and public opinion will react accordingly.