By Emily Stephenson and Ginger Gibson

EVERETT, Washington/WASHINGTON (Reuters) - Republican Donald Trump, who has made his criticism of a pending Pacific trade agreement central to his campaign, on Tuesday was to visit a Seattle suburb that is home to a large Boeing Co plane manufacturing facility that depends heavily on sales to Asian markets.

Trump's campaign has booked the Xfinity Arena, which seats thousands of people, in anticipation of a large crowd. The Republican presidential candidate, who has courted manufacturing workers with vows to tear up trade agreements, is due to speak at 7 p.m. Pacific Time (10 p.m. EDT).

The rally is likely to attract workers from Boeing, the world's largest aerospace company. Supporters of the 12-nation Trans-Pacific Partnership (TPP) point to Boeing's aircraft sales to Asia to tout the benefits of the agreement. Secretary of State John Kerry visited a nearby plant earlier this year to rally support for the pact.

Trump presents a conundrum for the unions who represent those workers. The unions agree with Trump on his opposition to TPP and the export of jobs overseas, but officials said they find his track record unconvincing.

"The fact is that Trump has had the opportunity to bring jobs to American, and he's chosen to outsource them," said Larry Brown, legislative and political director for the International Association of Machinists and Aerospace Workers District Lodge 751, which represents about 32,000 workers in the state, mostly at Boeing.

Boeing produces some of its largest planes only miles from where Trump will be speaking. As they are assembled, the painted tails of the planes show the airlines that ordered them, and many are Asian. Major components of each plane come from overseas: South Korea, China and Europe.

Over the next 20 years, Boeing projects that Asian customers will account for 40 percent of the total global jetliner's market, the company said in a recent report.

"Trade is a huge part of the success of manufacturing in Washington," said Linda Dempsey, vice president of international economic affairs for the National Association of Manufacturers, which Boeing belongs to. "They are exporting $73 billion in manufactured goods."

But Trump offers a more dire outlook, arguing that only he can keep Boeing from moving those high-paying manufacturing jobs from Washington to China.

"They'll start taking your business away, and you won't have much of Boeing," Trump told Seattle's KIRO radio on Monday.

RALLYING WORKERS

Trump has broken with the Republican Party's traditional embrace of free trade. He has vowed to rip up the TPP and renegotiate the North American Free Trade Agreement, or NAFTA, an existing deal with Canada and Mexico which he blames for the loss of U.S. jobs.

The Republican Party's support for free trade has put it in sync with large business groups such as the Chamber of Commerce and the National Association of Manufacturers.

Tony Fratto, a former official in the administration of Republican George W. Bush, criticized Trump as out of step with the party.

"Trump's policies in this area are really dumb generally, but are particularly dumb for a major exporting company," said Fratto, who worked on behalf of a coalition of large companies, including Boeing, that were pushing for renewal of the Export-Import Bank.

Visiting Washington state is also unlikely to get Trump much closer to victory on Nov. 8. Clinton leads by large margins in the state, according to opinion polls.

But voters there remain divided. Corey McNally, 40, of Whidbey Island, Washington, has not decided whom he will vote for.

"The union members love Hillary just because they're supposed to because she's a liberal," said McNally. And Trump, whom he called "just kind of a big show," may be too late to change anything.

"This company's been outsourcing jobs for years," he said of Boeing.

(Writing by Ginger Gibson; Reporting by Emily Stephenson in Everett, Washington; Alwyn Scott in Seattle and Ginger Gibson in Washington; Editing by Caren Bohan and Jonathan Oatis)