By Joe Brock

SEATTLE - Boeing factory workers will hold a large rally in Seattle on Tuesday to demand a better wage deal, mounting pressure on new CEO Kelly Ortberg to end a bitter strike that has plunged the troubled planemaker further into financial crisis.

Around 33,000 unionized West Coast workers, most in Washington state, have been on strike since Sept. 13, demanding a 40% wage increase spread over four years and halting production of Boeing's best-selling 737 MAX and its 767 and 777 widebodies.

The International Association of Machinists and Aerospace Workers (IAM) and Boeing leadership are locked in a paralyzing blame game over the strike, with both sides filing charges accusing the other of unfair labor practices during negotiations.

Boeing last week withdrew its latest offer, which included a 30% wage increase over four years, after talks also attended by federal mediators broke down.

U.S. Acting Labor Secretary Julie Su met with Boeing and the IAM in Seattle on Monday in a bid to break the deadlock, in her first in-person intervention.

Senator Maria Cantwell and Congresswoman Pramila Jayapal, both Democrats from Washington state, were due to speak at the rally at 12 p.m. PT (1900 GMT), the IAM said.

"This rally is more than just a gathering - it's our battle cry to the company that we are standing strong," the IAM said in a statement.

Its members have been holding smaller picket lines in front of Boeing sites throughout the strike.

Boeing announced last week that it would cut 17,000 jobs in a bid to shore up its finances and help to avoid its credit rating being downgraded to "junk" status. In mid-November, Boeing will send out 60-day notices to employees being laid off.

Investors and regulators have had Boeing under the microscope since a door panel flew off a near-new 737 MAX jet in midair in January.

Since then, the planemaker's shares have dropped 40%, the Federal Aviation Administration limited its 737 MAX production levels, hampering output even before the strike and its CEO was replaced.

(Reporting by Joe Brock in Seattle; Editing by Jamie Freed)