Southwest Airlines proposed building a $130 million terminal and parking garage at Boeing Field in Seattle, calling it "a nice, big, shiny, new, expensive gift" to the county that would boost employment, provide lower fares and even help sell Boeing jets.

The discount airline currently operates 38 flights daily from Seattle-Tacoma International Airport, but would increase service to 60 flights a day at Boeing Field in 2009, gradually rising to as many as 90 flights.

After 50 years, Southwest would deed the terminal and garage to the county. It also would pay fees, taxes and other costs while using the airfield, generating what it estimated at $1.6 billion in annual economic gains to the area.

"It's Christmas in July for King County, Seattle and Puget Sound," Southwest Senior Vice President Ron Ricks said in a sales pitch-style press conference at Boeing Field today.

"We're going to buy a lot of new Boeing 737s, and we're going to fly them to a building we built and gave to you," Ricks said.

If the proposal is accepted by King County, which owns the airfield, Southwest would transfer its service there in 2009.

Numerous obstacles remain, however, including concerns about the cost of road improvements and the potential for increased noise from the field. The Port of Seattle, operator of Sea-Tac airport, opposes any move by Southwest, and neighborhood groups in Seattle are also worried about noise and traffic.

The proposal may also set off a scramble among other airlines at Boeing Field.

Alaska Airlines said today that it, too, would like to operate as many as 100 flights a day from the airport near downtown Seattle if Southwest is allowed to move there.

Southwest said high costs at Sea-Tac are threatening its ability to serve Seattle, and without the move it might have to scale back operations here.

Costs at Sea-Tac are the highest among the 60 airports Southwest serves, Chief Executive Gary Kelly said. Southwest's nationwide average airport cost is between $4 and $5 per passenger. Sea-Tac costs amount to $10 per passenger, "with the cost destined to go higher," Kelly said. At Boeing Field, he said, Southwest thinks it can operate below its nationwide average cost.

Kelly said road improvements would be government's responsibility, but that the costs would be minimal, according to officials the company had consulted.

Southwest would conduct a full environmental review, and said its modern, all-Boeing fleet "climbs higher and climbs faster and thus diminishes the noise on the ground."

King County Executive Ron Sims said the offer would be carefully evaluated.

"At first glance, this appears to be a very generous proposal," he said in a statement.

"Southwest's proposal is refreshing considering that other corporations have sought hundreds of millions of dollars in public support for them to locate their facilities here."

But, he said, no decision has been made. The county aims to protect its pocketbook and ensure that concerns about noise and traffic are addressed.

"We will have a public process to hear directly from citizens of the region and will conduct a thorough environmental review that includes noise and traffic analysis, and do our best to minimize impacts on neighborhoods," he said.

"If those concerns are addressed, then we would commence a negotiation process in ... coming weeks and months."

Boeing spokeswoman Sandy Angers said the company doesn't have an opinion on a Southwest move to Boeing Field. "It's a Southwest and King County issue," she said.

But because Southwest currently operates a fleet of 417 Boeing 737s, Boeing does have a keen interest in supporting the airline's business.

"Southwest is a great 737 customer," Angers said. "Anything that's going to help them be profitable, we're all for their success."

Boeing Field is the delivery center for the narrowbody 737s, the place where airline customers come to pick up the keys and fly away the airplanes. Angers said that if Southwest were to make the move, she didn't anticipate any impact on Boeing operations at the airfield.