Boeing Co.'s sprawling aircraft assembly plant in Long Beach is in the running to build the aerospace giant's forthcoming 777X jetliner after a machinists union in Washington state rejected a deal that would have ensured the work would stay in the Seattle area.

Once considered a long shot, Long Beach is one of several cities under active consideration by Boeing after the International Assn. of Machinists and Aerospace Workers voted down a tentative labor agreement by a 2-to-1 margin late Wednesday.

Now Boeing, along with state and local officials, is in talks about the possibility of bringing the 777X program to Long Beach, where the company currently builds the C-17 Globemaster III cargo jet.

Gov. Jerry Brown has not yet commented on the program. But Brook Taylor, a spokesman for the Governor's Office of Business and Economic Development, said, "We are actively working to expand all facets of Boeing's operation in California."

Boeing has not discussed which locations it is considering, but reports suggest that possible manufacturing sites include Huntsville, Ala.; Charleston, S.C., where Boeing builds the 787; and Long Beach. The Seattle area hasn't been ruled out either.

After the union vote, the company said it would look at all options for a location to build the 777X, slated to be a more fuel-efficient version of its profitable twin-aisle aircraft.

"We are very disappointed in the outcome of the union vote," Boeing Commercial Airplanes Chief Executive Ray Conner said. "But without the terms of this contract extension, we're left with no choice but to open the process competitively and pursue all options for the 777X."

Moving the assembly line out of the Puget Sound region would be staggering to the Seattle area, where Boeing was founded in 1916. The 777 is one of Boeing's best-selling models. Versions of the plane have been built in Washington since the early 1990s, and the 777X is seen as vital to the company's fortunes in the long-haul market for decades to come.

The machinists union has estimated that the program could mean as many as 10,000 direct and 10,000 indirect industry jobs for the Puget Sound region alone.

The labor dispute in Seattle has drawn the attention of Southern California lawmakers, who are still reeling from Boeing's announcement in September that it intends to close the plane-making plant in Long Beach in 2015.

The site now houses construction of the C-17.

Southern California — the former undisputed center of the aerospace industry — has seen the number of aerospace workers in Los Angeles County fall to 56,780 last year, according to the Los Angeles County Economic Development Corp., which tracks the industry. That is a nearly 70% drop from the 189,035 workers employed in 1990.

Assemblyman Al Muratsuchi (D-Torrance), chairman of the Assembly's Select Committee on Aerospace, said he has reached out to Boeing executives to let them know that the state is interested in landing the 777X. He said he also planned to send a letter to Brown about securing the program.

"Time is of the essence," he said. "We have an opportunity here to bring thousands of jobs back home. This must be a priority."

Boeing has already moved some jobs from the Seattle area to Long Beach. The company announced in July that work performed by 375 people would be moved to Long Beach over the next year.

Less than a month later, Boeing said an additional 300 engineering support jobs would come to the region, and that a new engineering design center for commercial aircraft would be established.

Work in the aerospace industry is volatile and highly competitive. When Boeing said it preferred to build the 777X in Washington, it took state lawmakers less than a week to pass a package of bills that included $8.7 billion in tax savings for the company to build the plane there.

After that, Boeing gave the machinists union one week to make a decision on a labor agreement, which would extend the union's current contract eight years into 2024. But provisions of the agreement involving pension plans and healthcare benefits drew fierce opposition from union members and ultimately led to the workers' rejection of the labor agreement Wednesday.

The union represents more than 35,000 company workers.

Once the machinists union's unhappiness over the labor agreement surfaced, talk of Boeing's other options grew.

Meanwhile, aerospace experts pointed out that Boeing also has the option of manufacturing the jet in Charleston, S.C., where Boeing has a 787 assembly line. The site, the company's first nonunion final-assembly plant, was selected in 2009 — one year after a union strike stopped work in Washington for two months.

To win a contract to build the 777X, Long Beach may also try to woo Boeing by boasting about its workforce's decades-long experience building large aircraft.

The plant was built by Douglas Aircraft Co. during World War II. It thrived for decades, producing some of the world's most popular airliners, including the DC-3, DC-8 and MD-80. It still has a large "Fly DC Jets" sign nearby.

An Los Angeles County Economic Development Corp. official said the group is eager to help put together an incentive package to help bring the 777X to Long Beach.

"The region has a critical mass that can support aerospace firms," said Robert Kleinhenz, the group's chief economist. "The communities here in Southern California know how important the aerospace industry is to the local economy."

william.hennigan@latimes.com

Times staff writers Marc Lifsher and Christine Mai-Duc contributed to this report.