General Motors Corp. is trying to regain a share of the market for police cars, hoping its 2000-model Chevrolet Impala can give Ford Motor Co. a run for its money. But it may take some time before law enforcement agencies adjust to the new, front-wheel-drive sedan. GM is stepping up its marketing of the Impala to police departments across the country. Wiley said the vehicle was "designed for law enforcement from concept."