Chrysler Corp. will idle 18,300 workers when it closes three assembly plants for up to two weeks in January to cut stocks of some slow-selling compacts and intermediate models.

The nation's No. 3 auto maker said Wednesday it would shut the Hamtramck and Lynch Road facilities in Detroit and its Newark, Del., plant.

All three plants are also closed this week for inventory adjustment, and will stay down next week along with the rest of the industry for the traditional holiday vacation.

Chrysler's sales of compact 1978 Plymouth Volares and Dodge Aspens, and intermediates Plymouth Fury, Dodge Diplomat and Dodge Monaco and running behind the rate the company expected, according to reports.

The auto makers had a 95-day supply of unsold new cars as of Dec. 1, the trade journal Automotive News noted, compared with 50 1/2-day supply at General Motors Corp., a 55-day supply at Ford Motor Co. and an 82-day supply at American Motors Corp. A supply between 55 and 65 days is considered good.

Chrysler is counting on its two new subcompacts, the Dodge Omni and Plymouth Horizon, which go on sale next month, to boost its sagging sales.