King County Executive Ron Sims yesterday said it would be "unconscionable" for the Port of Seattle to delay or scrap light-rail service into Seattle-Tacoma International Airport should Southwest Airlines relocate to Boeing Field.

Port officials on Tuesday announced that $580 million in airport improvements are now in jeopardy, including roadwork that would bring the regional light-rail line into Sea-Tac.

In interviews yesterday, Sims, who sits on the Sound Transit board, which oversees planning for the light-rail line, lambasted the Port's actions as political posturing.

"It's an unconscionable decision. It's hostage-taking. It's not good public policy, and it's not appropriate," he fumed.

Sims said future growth at Sea-Tac, even without Southwest, justifies connecting light rail with the airport. And he said the competition created by Southwest's proposed move to Boeing Field would prove valuable to airlines and their customers.

"I've never seen a more flagrant foul against the free enterprise system," Sims said of the Port's threats.

Port officials said their inclusion of light rail on the list of possible cuts was not meant as a retaliatory strike against Sims or Sound Transit.

"We certainly don't want to lose something we've worked so hard to get," said Port Commission President Bob Edwards. But he said the airport was in a "highly uncertain time."

Edwards said Southwest's departure would mean changes to the projected growth at Sea-Tac and would affect many plans for improvements funded in large part by fees assessed to airlines.

The heated sparring between the Port and county is an unexpected turn after years of mass-transit planning. Light rail was supposed to reach the airport as part of Sound Transit's original plan for a 21-mile rail segment from Sea-Tac to the University District. But cost overruns forced the agency to scale back the project four years ago to a 14-mile line from downtown Seattle to a park-and-ride lot in Tukwila.

Last year, jubilant Sound Transit officials said they had discovered a way to make light rail reach the airport. But Southwest's efforts to move to Boeing Field because of higher costs at Sea-Tac may now place those plans in jeopardy.

Port officials said design work related to the light-rail connection will continue for now. But the project, along with many others, could be frozen if Southwest and other airlines depart and punch a hole in the budget for airport improvements.

Airlines remaining at Sea-Tac would have to pick up Southwest's share of the airport's $4.2 billion expansion costs, and they say their ability to absorb further costs is limited.

Dallas-based Southwest said last week it wants to build a new terminal at Boeing Field and run up to 85 daily flights there, compared with 38 now at Sea-Tac, to avoid the cost of Sea-Tac's 10-year expansion. Alaska Airlines has said it, too, may consider moving some flights to Boeing Field if its competitor moves.

Jim Brunner: 206-515-5628 or jbrunner@seattletimes.com

Seattle Times staff reporter Eric Pryne contributed to this report.