OLYMPIA — The state Senate yesterday narrowly approved an $8 billion transportation plan that would raise gas taxes by 9.5 cents over four years and spend billions on transportation projects in the central Puget Sound region, including the Alaskan Way Viaduct.

The package would raise the gas tax by 3 cents a gallon the first year, 3 cents the second year, 2 cents the third year and by 1.5 cents in the fourth.

It includes $2 billion for the viaduct, $992 million for Interstate 405 and $500 million to help replace the Highway 520 bridge over Lake Washington.

The measure passed 26-22 and now goes to the House. If it becomes law, this would be the largest gas-tax increase in state history.

It's not clear how the bill will fare in the House. Democratic leaders there say they need some Republican votes to pass a package, and Republicans aren't making any promises.

Gov. Christine Gregoire has indicated she supports the measure and was actively working yesterday to get it passed in the Senate.

Both parties are under growing pressure to act.

A coalition of businesses, labor unions, local government and environmental groups — which calls itself the Transportation Partnership — is aggressively lobbying for a package.

The package would not fully pay for replacing the viaduct and 520 bridge. The central Puget Sound region would have to contribute billions of dollars as well.

The plan that passed the Senate would require the region to come up with its share of local money by January 2007 or risk losing funds for projects.

There were concerns yesterday and earlier in the week that Senate Republicans would derail the package. They had complained about the amount of money being spent on the viaduct compared with other projects, and the lack of money for performance audits.

Republicans also said they were worried over rumors that House Speaker Frank Chopp was trying to sabotage the package and would only support a 3-cent gas-tax increase.

They wanted an assurance that Chopp would allow the House to vote on the measure.

Chopp yesterday denied he was working against the package, saying he supports the House transportation plan, which is much like the Senate's.

He would not promise a vote on the Senate plan, however, adding he wants to make sure the bill has enough Republican support.

Chopp said he didn't have a firm number, but that 18 Republican votes are "what we've been talking about."

Some prominent House Democrats aim to force a vote on the package, no matter what. House Appropriations Chairwoman Helen Sommers, D-Seattle, told Senate Republican leaders yesterday she would not allow the state's $26 billion, two-year operating budget to move forward without that vote.

The fact that seven Senate Republicans ended up voting for the Senate bill should help in the quest for GOP votes in the House, Murray said. "That's a good vote."

He said House Democrats might be able to deliver up to 35 votes, which means they'd need at least 15 Republicans to join them in passing a bill.

Democrats want a bipartisan vote to avoid taking a hit next election for supporting a gas tax. Last election, a Republican political group sent out campaign fliers attacking lawmakers because they voted for a nickel increase in the gas tax in 2003.

House Republican Leader Bruce Chandler, R-Granger, said his party could deliver some votes, but he wouldn't guarantee how many.

There were Democrats and Republicans who voted against the Senate's transportation tax package.

Sen. Jim Hargrove, D-Hoquiam, said he opposed it because people in rural communities have to drive longer distances than those in urban areas like Seattle.

"Rural families pay a much larger proportion of their income [for gas]," he said. "It's a regressive way to fund transportation."

Sen. Jim Honeyford, R-Sunnyside, agreed, arguing "We're putting a heavy burden on rural residents."

Several dozen members of the coalition supporting the gas-tax increase converged on the Capitol earlier this week to meet with legislators and Gov. Gregoire's senior staff.

Labor and business supporters said they wanted to give lawmakers some peace of mind that voting for a big gas-tax increase wouldn't cost them in the next election.

"We're trying to reassure senators and representatives that we're going to be there to back them up and to kind of counter the talk-show chatter," said Jared Smith, area manager for Parsons Brinckerhoff, a construction-management firm.

Labor leaders, who last week were in the middle of a huge fight with business over changes to the state's unemployment-insurance system, yesterday worked side-by-side with their business counterparts.

"There are times when you need to work together to create family-wage jobs and build a stronger economy," said Rick Bender, president of the Washington State Labor Council. "This is a huge project. It'll put a lot of people to work — in the tens of thousands."

Environmental leaders also helped with the last-minute push. Clifford Traisman, a lobbyist for the Washington Conservation Voters and the Washington Environmental Council, said environmentalists were reluctant to support past transportation packages because they did not put enough emphasis on mass transit.

But Traisman said he is confident his group's concerns will be addressed this time.

"It's a different dynamic than in past transportation pushes," said Traisman. "It's been far more collaborative."

Andrew Garber: 360-943-9882 or agarber@seattletimes.com