LONG BEACH, Calif. — Boeing Co. said yesterday it would start shutting down production of its cavernous C-17 military cargo plane, marking the possible end of aircraft manufacturing in a region that once dominated the industry.

Unless Congress authorizes new orders, the decision could trigger a ripple of job cuts nationwide, including more than 7,000 Boeing employees and an additional 25,000 workers in 42 states that provide parts for planes still moving everything from tanks to troops around Iraq and Afghanistan.

Layoffs would not likely be immediate — Boeing has several dozen pending orders, enough to keep production into 2009. But the Chicago-based company said yesterday it would no longer spend tens of millions of its own dollars making planes that may never be sold just to keep the supply lines open in hopes of new business.

"I think we all knew it was coming," said Dwight Parker, an engineer and 25-year veteran of Boeing. "There was a part of me that was holding out for some surprise announcement."

Nicknamed the Globemaster III, since it first flew in 1991 the C-17 has been valued for its ability to land on short dirt runways such as those overseas or during disaster relief. These flying warehouses played a major role airlifting supplies into areas devastated by last year's Gulf Coast hurricanes.

Congressional leaders have been lobbying to extend C-17 production and added money for three more of the aircraft in the 2007 defense spending bill, which has not yet passed the Senate. Boeing said it could keep the program if Congress funds at least 10 more planes, though a delay would increase costs above the current price tag of about $200 million each.

"We haven't given up," said Ron Marcotte, vice president and general manager of Boeing Global Mobility Systems.

There is some political will to salvage production.

The Long Beach plant is the last major airplane factory left in Southern California — earlier this year, Boeing delivered its last 717 passenger jet from a sprawling complex of buildings that has been churning out planes since the 1930s. Workers have assembled 15 of the planes each year in a hangar big enough to fit several C-17s at once.

Though far from past levels, aircraft production still provides thousands of high-paying jobs.

"This is the last Californian aircraft on a line that will be dying in an election year," said Richard Aboulafia, an aerospace analyst at the Virginia-based Teal Group, an aviation consulting group. "I can't imagine Congress won't come through."

Boeing's shares fell 97 cents or 1.2 percent yesterday to close at $77.62 on the New York Stock Exchange.