General Motors Corp. announced yesterday that it temporarily will lay off about 9,000 workers this month in an inventory-reduction move affecting five of its U.S. plants.

About another 4,000 workers at the plants will be shifted to job training during the layoff periods, which will run from one to two weeks on a staggered basis, beginning this week.

The affected plants include two facilities in Pontiac, Mich., where GM builds its two-seater Pontiac Fiero and its rear-wheel-drive Oldsmobile Cutlass and Buick Regal models; Lakewood, Ga., the assembly site for GM's old, rear-wheel-drive Chevette and Pontiac 100 subcompacts; Van Nuys, Calif., an assembly site for the Chevrolet Camaro and Pontiac Firebird; and a Flint, Mich., plant that also builds the Cutlass and Buick Regal.

GM officials said yesterday that the decision to idle production workers does not indicate an overall downturn in the U.S. automotive market. Nor are the layoffs indicative of any long-term difficulties the company is having with the affected products, the GM officials said.

"This is no more than a normal, temporary adjustment to control and maintain our inventory. It's pretty standard procedure," said Donald Postma, spokesman for GM headquarters in Detroit.

"None of these people is being laid off permanently," Postma said.

However, for months now, auto industry analysts have been expressing concern that GM has been overstocking its supply lines, perhaps in a calculated move to increase its sagging, but still dominant, share of the U.S. market.

But now, largely as a result of its aggressive building program, GM has a more than 100 days' supply of the cars whose production will be held in abeyance, according to wire service reports based on information from Ward's Automotive Research, an auto industry research service based in Detroit.

A 60- to 65-days' supply of cars is considered normal in the domestic car industry.

The oversupply of GM products is affecting dealers in the Washington metropolitan area. But Steve Smith, owner of Steve Smith Pontiac in Fairfax, said he is not worried by the glut.

"We're not having any problem moving the cars, although we do have about 77 Fieros on hand," Smith said.

"GM just loaded all of its dealers up with cars in the winter. But they're beginning to move now that we're approaching spring," which usually is a major car-buying season, Smith said.

For example, Smith said his dealership sold nine Fieros in December, 20 in January, 20 in February, and that he expects to sell about 35 Fieros a month during the spring selling season, which roughly stretches from the middle of March until the end of June.

Fieros carry base prices ranging from about $8,949 to $10,595.