DETROIT — Two Japanese automakers are scaling back production at North American plants as they assess their ability to get parts from Japan after that country’s devastating earthquake and tsunami.

Subaru of America said Tuesday it has suspended overtime at its only North American plant in Lafayette, Ind. Toyota Motor also said it was suspending overtime and Saturday production at its 10 plants in the region.

So far, other Japanese automakers say their North American plants are unaffected. Nissan Motor, Honda Motor, Mitsubishi Motors and Mazda Motor all say they have not changed their production plans.

But that could change if lingering damage from the earthquake prevents parts shipments. Mitsubishi, for example, has enough parts on hand or en route to operate its Illinois assembly plant through April 3, spokesman Dan Irwin said.

In Japan, auto companies have shut down production for the rest of the week as they assess damage to plants, ports and roads.

While Japanese automakers with North American plants use locally-based suppliers for many of their parts, others still come from Japan. The U.S. imported $12 billion worth of auto parts from Japan in 2010, from spark plugs to engines, according to the Original Equipment Suppliers Association.

Dave Andrea, the trade group’s senior vice president of industry analysis and economics, said some parts had been in short supply before the earthquake, including semiconductors, precision bearings and tires. He estimated that most automakers have a three- to four-week inventory of parts in the pipeline.