With credit drying up and new-vehicle sales slumping to a 25-year low, car dealerships from New Jersey to California are going out of business at an accelerating pace, threatening greater economic pain for communities around the country.

The National Automobile Dealers Association estimates 700 new-car dealerships will close this year, up from 430 last year, and taking with them an estimated 37,100 jobs. That is a heavy blow to a key piece of the U.S. economy. The country's 20,700 dealerships accounted for $693 billion in...