Robert C. Stempel A New Team Spirit At General Motors The selection of Robert C. Stempel as chairman of the General Motors Corporation speaks volumes about the new priorities of the world's largest auto maker. Since the 1950's, G.M.'s management had been dominated by financial executives whose bottom-line orientation took precedence over quality, market share and other concerns. The latest exemplar of that philosophy was Roger B. Smith, an accountant whose tenure as chairman ended in August. The 57-year-old Mr. Stempel has a background as an engineer and a sympathy for the importance of vehicle design and manufacture. His ascension could not come at a more opportune moment for G.M., whose vehicles usually fail to match the best Japanese cars in quality and customer surveys. With car sales down in 1990 and another weak year predicted, G.M. will have to work hard to regain some of the huge market share it lost in the 80's.