Pierce County Executive John Ladenburg said yesterday he will ask the Puget Sound Regional Council to oppose Southwest Airlines' proposed move from Seattle-Tacoma International Airport to Boeing Field.

Ladenburg, who serves as president of the four-county planning group, said the move supported by King County Executive Ron Sims throws into question the council's decision more than a decade ago to accommodate airline growth with a third runway at Sea-Tac.

"I think a lot of blood was spilled in all the decisions over Sea-Tac. We can't just let one or more airlines change our decisions by running off to another airport," Ladenburg said.

"We certainly shouldn't let some corporate headquarters in Dallas tell us where we're going to have our transportation hubs."

If commercial air traffic is allowed at King County-owned Boeing Field, Ladenburg said, it should be supported by the same kind of "multibillion dollar" investment in roads and sound-proofing of nearby homes that has been made around Sea-Tac Airport.

Southwest announced plans Thursday to spend $130 million on a new terminal and parking garage that would allow it to operate up to 85 flights a day out of Boeing Field. Rival Alaska Airlines said it, too, wants to move many of its flights to the county airport.

Sims said he has no intention of turning the county airport into a rival to Sea-Tac.

"I think we're going to be able to show we have a response to any concerns that they have," he said. "I think it's going to be difficult to argue the sky is falling, because that's not going to be the case."

Boeing Field won't require investments comparable to Sea-Tac's third runway because the volume of air traffic will be much smaller, Sims said.

"We hear what I consider to be fairly outlandish demands for new investment in transportation there. I'm saying, 'Folks, we're 10 times smaller than Sea-Tac,' " he said.

Ladenburg has asked the regional council's staff to draft a resolution opposing Southwest's proposed move. He said he will refer the resolution to the Transportation Policy Board chaired by King County Councilwoman Julia Patterson.

Patterson, who hails from Sea-Tac airport's hometown of SeaTac, is co-sponsoring a Metropolitan King County Council ordinance to require airlines to pay all costs — including roads — associated with a move to Boeing Field. The Southwest move requires County Council approval.

The airlines' desire to leave Sea-Tac shows they couldn't afford the third runway, Patterson said.

Now the region faces a difficult question, Patterson said: "Is it appropriate for the government to interfere with the natural inclinations of the airlines to try to provide as affordable service to the public as possible, knowing that that decision may result in the spread of noise pollution and the resulting neighborhood blight?"

Keith Ervin: 206-464-2105 or kervin@seattletimes.com