SPRING HILL, Tenn. -- General Motors will idle the Spring Hill assembly plant and its 2,500 workers later this year, but United Auto Workers officials said the facility is also in the running to build the next generation small car for the U.S. automaker.

Workers were told the shutdown will occur in the fourth quarter and production of the Chevrolet Traverse crossover SUV will move to Lansing, Mich., said Todd Horton, a longtime United Auto Workers Union worker and editor of the newspaper for Local 1853.

Horton said GM told workers it doesn't know how long production will be shut down and that resumption will depend on market conditions.

Union officials said they were disappointed because the plant's future is uncertain in a troubled economy.

But they were relieved that Spring Hill wasn't one of nine plants GM announced it will close. The automaker filed for Chapter 11 bankruptcy protection Monday.

"This is not as bad as it could be," said Mike Herron, the chairman of UAW Local 1853's bargaining committee.

"I'm an optimist. We would have preferred the Traverse continue to be built. The absolute worst would be a plant closure," he said.

Instead, Spring Hill is expected to compete with another idled production plant in Orion, Mich., for the right to build a new subcompact car that GM considers key to the company's survival.

Herron thinks Spring Hill may have a leg up because the recent retooling to build the Traverse gave the plant the most modern equipment in GM.

"There's a billion dollars worth of equipment put in this place over the last 18 months," Herron said.

Herron points to another advantage. The UAW local and Spring Hill work force have agreed to operate the plant seven days a week without overtime, he said.

The plant has had more flexible work rules than others, thanks to its history. Car production began there in 1990 with the Saturn, GM's small-car answer to Japanese competitors. The factory made more than 3.7 million vehicles for the Saturn brand until 2007, when it shut down for the Traverse retooling.

Full-scale production of the Traverse started in October 2008.

GM said the stamping, polymers, service parts and Powertrain operations at Spring Hill will continue.

State Sen. Bill Ketron, a Republican from Murfreesboro whose district includes Spring Hill, said GM officials told him the plant will phase down to 604 employees when assembly production ends.

"I am concerned for the well-being of all the employees at Spring Hill. I'm concerned about Maury County in general. How will this affect our revenue stream, which is already down $100 million this past month? It's got to hurt," Ketron said.

U.S. Sen. Bob Corker, whose role in federal government bailout talks has been criticized by the UAW, said he's disappointed for all the Tennessee families affected by Spring Hill's uncertainty.

"On the other hand, I am glad there are going to be at least 600 jobs there and the plant is not going to be closed, but idled," Corker told The Associated Press shortly after the announcement.

"We are going to continue to work with GM and Gov. (Phil) Bredesen to do everything we can to see that that plant ends up being utilized."

U.S. Sen. Lamar Alexander spoke with Channel 4 about the future of the Spring Hill plant.

"GM's decision to put its Spring Hill plant on standby is a blow to many employees who work there and to their families, but hopefully it will only be a short-term problem. I have discussed with Gov. Bredesen how I can be of as much help as possible to those affected," said Alexander.

Channel 4 has team coverage on how the bankruptcy is affecting Spring Hill and Maury County. Watch Channel 4 News at 5 and 6 p.m. for more details.