Hospital stays of a week or longer due to car crash injuries have dropped 43 percent in Michigan since the state's safety-belt law went into effect in July 1985, according to a University of Michigan study.

Alexander C. Wagenaar, who directed the study, said there also has been a 19 percent reduction in the number of car crash victims admitted to hospitals and a 20 percent reduction in the rate of crash victims admitted with injured arms and legs. He also reported a 19.7 percent drop in auto crash fatalities.Since December 1984, the research teams at Michigan have observed more than 205,000 vehicle occupants at survey points throughout the state to determine the use and efficacy of safety belts.