Other automakers, such as Ford Motor Co., have already instituted such arrangements on a plant-by-plant basis.

'We've been doing that over many of our assembly plants over the last 2 1/2 years,' said Ford spokeswoman Anne Marie Gattari. 'There are several benefits.'

Automakers running plants below capacity can save on electricity and other costs by running the equipment longer for four days, then shutting down on the fifth, Gattari said.

Any maintenance can be done on the fifth workday, not on the weekend when it would be more expensive, she said.

'It's better for employees, too,' she said. 'He or she can spend more time with their family. They're not driving as much, so they can save fuel themselves.'

Chrysler's Saenz said he believed the company's workers would go for such a deal.

'I would think a majority of our employees, given the option, would be in favor of it,' he said.

The UAW could not be reached for comment.

But some industry experts say Chrysler's initiative might be an ominous sign for workers.

Gary Chaison, professor of industrial relations at Clark University in Worcester, Mass., said that if he were a worker, he would be concerned.

'It means that a plant is producing a product for which there is little demand,' he said.

'It makes sense to Chrysler,' he said of the shortened workweek, 'as an early stage of trying to shut down these plants. It can only be interpreted as very discouraging news.'

Chrysler, which has a preponderance of trucks and SUVs in its model range, has been hurt badly by a steep downturn this year in the U.S. auto market and a dramatic shift away from gas-guzzling vehicles.

So far this year, Chrysler's sales have fallen more than those of any other major player in the U.S. auto market.

Chrysler's car and truck sales are down 22.8 percent for the first seven months of the year, compared with an industrywide decline of 10.5 percent.

Saenz said the automaker's effort to shorten the workweek would affect most plants -- but not those producing small cars or other vehicles in high demand. He said the arrangement would not be proposed for the Belvidere, Ill., and Sterling Heights assembly plants.

The Dodge Caliber compact and two small SUVs, the Jeep Patriot and Compass, are produced at the Belvidere plant. The Sterling Heights plant turns out the Chrysler Sebring sedan and convertible and the Dodge Avenger, all midsize sedans.

Saenz said a pilot program will be rolled out this week at a parts distribution center in Atlanta. Chrysler would not comment on how much it would save if the plan were implemented.

GM spokesman Tony Sapienza said GM does not have plants running on four-day workweeks in North America and has not been approached by the UAW to institute such an arrangement.

Most automakers, including the Japanese, are scaling back their output in the United States, where the market is on track to end this year at the lowest level in more than a decade.

Other automakers have used four-day workweeks for other reasons. Volkswagen AG implemented them in Germany 15 years ago but that was in a bid to save jobs at the then-troubled automaker.