Board members said trains would attract more travelers and move them faster than a combined bus-and-transit option.

The 11-mile Eastside line, with service to Bellevue, the Microsoft campus and downtown Redmond, is the biggest piece of a regional transit package that King, Pierce and Snohomish county voters will be asked to approve next year. The plan also would extend light rail north to Lynnwood and south to the outskirts of Tacoma.

Current scenarios call for the longest possible light-rail line, with less money for long-distance commuter trains and express buses. The total cost could reach $10.8 billion in today's dollars, with $6.9 billion coming from new sales taxes and the rest from prolonging existing sales and car taxes.

"We need to look at the cost of not doing it," said Mary-Alyce Burleigh, a Kirkland City Council member on the transit board. "The cost to economic growth, the cost in time, and the cost in congestion, if there is no other option. Light rail will give us a choice."

The three proposals released for public review are:

-Extending light rail to Northgate, Bellevue and Kent, for a sales-tax increase of 3 cents on a $10 purchase.

-Extending service to Mountlake Terrace, Overlake and Federal Way, 4 cents on a $10 purchase.

-Paying for tracks to Lynnwood, Redmond and the Port of Tacoma, 5 cents tax on a $10 purchase.

Voters may be asked to double their current Sound Transit taxes. The transit board voted to drop its do-nothing and low-cost options, ensuring the request will be at least $75 a year for a typical household, and as much as $125 per year if the plan is approved in its entirety.

Sound Transit is nearing the halfway point on its first Seattle light-rail line, from downtown Seattle to Seattle-Tacoma International Airport. That project was approved by voters in 1996.

Earlier this year, the Legislature approved a bill requiring that for the transit plan to pass, voters must approve a multibillion-dollar regional highway plan next year.

Meanwhile, King County Executive Ron Sims is proposing a sales-tax increase this fall for more Metro bus service, while Seattle Mayor Greg Nickels is pushing a 20-year, $1.8 billion measure for city bridges, roads and trails.

The Eastside line would run on what are now the I-90 express lanes, across the floating bridge and Mercer Island, then north into downtown Bellevue. A related proposal would squeeze new high-occupancy vehicle lanes into the existing shoulders of the bridge.

From downtown Bellevue, the line would parallel Highway 520 to Microsoft's headquarters, ending in downtown Redmond. The alignment could include a downtown Bellevue tunnel, or elevated tracks that cost about $400 million less.

Project opponent John Niles, of the pro-bus Coalition for Effective Transportation Alternatives, said the tracks will make traffic worse for buses, van pools and general traffic bound for other locations. The coalition estimates that just 15 percent of downtown Bellevue commuters cross the lake.

Also Thursday, the Port of Seattle announced that Woodinville-based Mowat Construction had won the first of three contracts to extend light rail to Sea-Tac Airport with a low bid of $93.4 million. The work involves relocating roads to accommodate about a mile of light rail along the airport expressway.