By Jonathan Kaminsky

OLYMPIA, Washington (Reuters) - The leader of Boeing Co's (BA) main union in Washington state faces a revolt that could complicate efforts to bring the new 777 jetliner to the Seattle area, as the airplane maker moves to consider alternative buildings sites for the revamped plane.

Boeing formally launched the new 777, formerly codenamed 777X, on Sunday with 259 orders worth more than $95 billion at list prices - the largest combined order in its history. The jet is due to enter service around 2020.

Boeing Chairman and Chief Executive Jim McNerney told reporters in Dubai on Monday that the company expects to make a decision on where to build its newest jet within 3 months.

"We will be announcing within the next two- to- three months very specifically plans for manufacturing," he said. "We have a number of alternatives and we are in the process of considering them."

The company said it hasn't changed the timing of the aircraft's arrival, and that it is negotiating with other states after the International Association of Machinists and Aerospace Workers union rejected a contract offer that Boeing said was necessary for the jet to be built in Washington.

Boeing officials were on planes to other states the day after the union vote. The proposed labor deal, which would have extended the workers' current contract ending in 2016 for eight years, included cuts to pensions and health care benefits, a slower rate of wage increases for new workers and a $10,000 cash bonus per member.

Brokered between Boeing executives and IAM union leaders in about five weeks, the contract extension was voted down by a 2-1 margin on Wednesday, with dozens of workers at the Seattle union hall jeering their leadership as sellouts after the results were announced.

After the vote, several union members said they had lost confidence in IAM District 751 President Tom Wroblewski, who helped negotiate the deal, then called it "a piece of crap" at a union meeting, and then wrote a letter to members calling it "an opportunity we will never see again to secure thousands of good-paying jobs."

In the days after the vote, two of the four local IAM units in the Puget Sound area passed votes of no confidence in Wroblewski and called for his resignation, said a union official with knowledge of the votes.

Union spokesman Bryan Corliss said that Wroblewski was travelling this week on union business and would not be available for an interview.

Corliss said he knew of no plans for Wroblewski to step down, noting that he was reelected to a four-year term in 2012.