General Motors joins rival Toyota in suspending some U.S. vehicle production due to the disaster in Japan, with the Detroit auto maker halting its Shreveport, LA, assembly plant for a week beginning March 21.

GM cites a parts shortage for the shutdown at Shreveport, which makes the Chevrolet Colorado and GMC Canyon small pickups. The plant, which faces closure in 2012 if it does not win a new product, presently operates on one shift.

According to Ward’s data, stocks of the Colorado and Canyon finished February with a 58 and 61 days’ supply, respectively. The industry norm is 60 days.

The auto maker says in statement, “At this point, we have sufficient vehicles to meet customer demand.”

GM adds, “Like all global automakers, we will continue to follow the events in Japan closely to determine the business impact, working across the organization to maximize flexibility, supply the most critical operations, and effectively manage cost.”

Toyota said March 15 it would suspend overtime and Saturday work at all of its North American assembly plants to conserve parts.

Major automotive suppliers Aisin Seiki and JATCO, which provide parts to a long list of global auto makers, suspended production at their plants in Japan this week after an earthquake and tsunami hit the country on March 11.

Japanese auto makers and their captive suppliers in Japan stopped production almost immediately to focus on the crisis.