The news of Philips N.V. spending $20 million on the postwar expansion of its three war-working U.S. plants has set U.S. electronics industry on edge.

Quietly last week, the North American Philips Co., Inc. announced that it will spend $20 million on the postwar expansion of its three war-working U.S. plants (at Dobbs Ferry, Mt. Vernon, N.Y., and Lewiston, Me.). This was not a dazzling amount of money. Yet the news set the whole $3½-…