DETROIT  Chrysler said Wednesday that it would close all 30 of its factories for at least one month, starting at the end of this week, in response to plunging vehicle sales in the United States.

The company said the plants, which employ 46,000 union workers, would resume production no sooner than Jan. 19. Some will remain closed for several more weeks. Normally, the Detroit automakers close their plants for about two weeks at the end of the year.

In addition, Ford Motor said Wednesday evening that it would extend the holiday shutdown at most of its plants to a third week.

Meanwhile, worries that Chrysler could be forced to file for bankruptcy have spooked many auto dealers into borrowing so much money from the automaker’s lending arm that the company said it might need to suspend the loans.