WASHINGTON — Northwest Airlines mechanics walked off the job last night and early today after months of negotiations failed. The airline promised to continue to fly its planes by using replacement workers and reassigning managers.

Jim Young, spokesman for the Aircraft Mechanics Fraternal Association (AMFA), said union members would rather see the airline go into bankruptcy than agree to Northwest's terms. The union, which represents 4,427 of Northwest's 40,000 workers, including 123 in the Seattle area, decided to strike at 12:01 a.m. East Coast time today.

Shortly after the strike began, representatives of the AMFA Local 14 dropped off around 100 picketers at three sites around Seattle-Tacoma International Airport.

A handful were in front of a door on the arrivals level, in front of the Northwest ticket counter; others were at the flag pavilion at the entry to the airport. The majority were in front of the Northwest hangar.

The picketers didn't appear to disrupt flight operations. Check-in for Flight 222 to Detroit proceeded as usual, and the flight was due to depart on time, at 10:35 p.m.

Iruka Amamilo, 21, of Seattle, said she was en route to New Orleans through Detroit. She had been worried the flight would be canceled "because I was supposed to leave earlier today but I missed my flight."

Once she had her ticket and was checked in, she felt more comfortable but was still concerned about her connecting flight.

"Hopefully it's not going to be a problem," she said.

Mike Prentice, strike coordinator for AMFA Local 14, said his union was awaiting word on whether the Northwest flight attendants union would join the group.

"The rumor is they're going out [picketing] with us," Prentice said.

But as the strike began, the mechanics still were without allies. Other unions had not publicly stated their intentions to honor picket lines. Flight attendants, considered the most likely to offer support, were voting on whether to honor a picket line. Northwest earlier yesterday sought a court injunction to block the move, and has said it expects other workers to be on the job as usual.

Other unions were waiting for word before revealing whether they would cross a picket line or tell their members to report to work.

Bob Parker, a spokesman for Sea-Tac Airport, said Northwest averages about 36 daily departures from Seattle.

He said local AMFA representatives have permission from Sea-Tac to establish picket lines at several spots throughout the airport: at the flag pavilion on the way into Sea-Tac; at the curbside, where passengers enter and exit the airport; and at the skybridges between the airport and the main parking garage.

Sea-Tac authorities will monitor the strikers' activities to ensure they don't impede normal operations.

"There's no reason there should be any airportwide impacts," Parker said. "This should be limited to Northwest."

Several mechanics at Northwest's biggest hubs, in Minneapolis-St. Paul and Detroit, said they were told to leave before the strike began. They were ordered to surrender their employee identification badges and were escorted off the property by private security guards. A Northwest spokesman confirmed the claims.

The standoff promises to greatly reshape the airline.

Unlike a 1998 strike by pilots that grounded Northwest for nearly three weeks, the airline claims it can continue to operate normally by tapping 1,200 replacement workers and hundreds of managers to maintain its planes. Northwest also will deploy outside vendors to work at its cities outside its hubs in the Twin Cities, Detroit and Memphis, Tenn.

Union mechanics believe the plan will fail, stranding and delaying passengers as flights are delayed and canceled. Northwest has warned that scenario could force it into bankruptcy.

Union and company negotiators reconvened at National Mediation Board headquarters in Washington at about 9 a.m. Eastern time yesterday in a last attempt to reach a contract agreement. Union officials had spent the night studying a "last and best" contract proposal from Northwest.

Northwest on Thursday night had handed over a proposal that the mechanics said was far from what was needed for a deal. The company had not budged from the $176 million in wage and benefit cuts, according to the union.

Negotiators for the mechanics were working on "what probably will be our last-ditch effort to get a deal done," Steve MacFarlane, assistant national director of AMFA, said yesterday afternoon.

Northwest has reported operating losses of more than $3 billion since 2000 and has watched its rivals win pay cuts from workers by either threatening or actually filing for bankruptcy. Now, saddled with the highest labor costs in the industry, the airline says it needs to cut annual labor costs by $1.1 billion.

Pilots and salaried workers had agreed earlier to combined cuts of $300 million, but the company's efforts have bogged down with three other major unions.

To its mechanics union, the airline earlier had proposed cutting pay by 25 percent and eliminating half of remaining jobs to arrive at a $176 million annual cost-cut target. The union countered this week with a proposal it said met the $176 million target and preserved jobs; but the airline claimed it fell $76 million short.

Julie Hagen Showers, Northwest's vice president for labor relations, said the company's final offer was fair and equitable.

"AMFA was unable to meet the saving targets we needed," she said.

Details of revised proposals were not available late yesterday.

As rhetoric has heated up during the past few weeks, Northwest has tried to reassure customers that it would be business as usual today no matter how things went at the bargaining table. It has invested 18 months and tens of millions of dollars in a plan to recruit and train replacement workers.

As the strike loomed, some Northwest passengers worried.

"I'm concerned about getting back here," said Drew Johnson, 24, of St. Paul, who was planning to travel with four friends to Los Angeles for vacation and return next weekend. "I'm still a student, and I'm moving to Oklahoma as soon as I get back. It could affect all of my plans."

Mechanics for Mesaba Airlines — who had indicated that they would honor a picket line by their colleagues at Northwest — were stopped by a federal judge yesterday. U.S. District Judge David Doty granted a temporary restraining order sought by the regional carrier, which flies Northwest passengers from smaller cities to its hubs.

Some mechanics had thrown in the towel on a negotiated deal long before the deadline. Paul Volker, a mechanic with Northwest for 26 years, was headed yesterday to a friend's cabin for the weekend even though he was scheduled to work at 6:18 a.m. tomorrow. Volker didn't expect to be back at work. He had watched Northwest prepare too long and hard for a strike.

"I've just seen too much preparation going into the plans for a strike," he said. "You buy the beer, you buy the chips, you rent the hall, you have the party."

Compiled from Knight Ridder Newspapers and The Associated Press; Seattle Times aerospace reporter David Bowermaster also contributed to this report.