In another sign the U.S. market downturn is affecting more than just Detroit, Toyota Motor Engineering and Mfg. North America Inc. plans to close its U.S. and Canadian assembly plants for two days in December to rein in inventories.

The shutdowns, slated for Dec. 22-23, will trim production some 10,300 vehicles, according to a Ward’s estimate.

Toyota will slow output at three plants in 2009, cutting half or more of the 500 temporary workers at its Georgetown, KY, plant and slowing the line speed in the first quarter from roughly 65 cars per hour to 52 hourly. No permanent workers will be idled by the move.

It also will cut in half Sienna minivan production in Princeton, IN, beginning January, though it will not idle any workers on the plant’s two shifts. Spokesman Mike Goss says it hasn’t been determined how Toyota will split the production between the two shifts.

The second shift on the Tacoma pickup line at the New United Motor Mfg. Inc. joint venture with General Motors Corp. in Fremont, CA, also will be eliminated as of January. No workers will be furloughed as part of the move, Goss says.

Maintaining production in December is Toyota’s Baja California, Mexico, plant, where Tacoma pickups are built. Goss says the auto maker’s deal with the Mexican government requires it to produce 50,000 of the trucks this year and it needs the extra two days to hit that target. Toyota plans to keep the plant’s output at the 50,000-unit level in 2009.

Production also will be cut at Toyota’s component operations as a result of the scaled-back vehicle output, but Goss says no other workers will be idled.

Toyota’s U.S. sales fell 29.4% in October, and it ended the month with a 68 days’ supply of domestic cars in inventory, plus 113 days’ of light-truck stocks. Tacoma inventories stood at 119 days’ and Toyota had an 83-day supply of Sienna vans and 70-day stock of Camry sedans.