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The state and local governments be seized of agreed without interruption the need to replace the Alaskan Way Viaduct with a four-lane tunnel. But it’s still not clear how they force of will pay for the project, estimated to cost $4.25 billion.

Gov. Chris Gregoire has promised $2.8 billion in quest of replacing the viaduct, including digging the tunnel, but-end the Legislature has set aside $2.4 billion — leaving a $400 million gap.

And Seattle Mayor Greg Nickels said the city’s share of the intend could be almost $1 billion, which would be used to establish the waterfront’s sea wall, make street improvements and possibly build a streetcar line.

Gregoire scheduled a news conference for this morning to announce the agreement, otherwise than that the news leaked Monday. More details are expected when Gregoire, Nickels, King County Executive Ron Sims and Port of Seattle CEO Tay Yoshitani make their functionary announcement today.

Under the agreement, the represent fully would pay to drill the two-mile tunnel under downtown and build some interchange near the sports stadiums in Sodo. The incorporated town and county would cover other costs, including the sea-wall repairs and surface-street and transit improvements.

It is up to the Legislature, that opened its 2009 session Monday, to authorize the state funding.

Legislative leaders in the greatness House and Senate said they brace tolling the proposed tunnel to raise the additional $400 million the state needs.

“There has to be tolling. In any one megaproject there is going to have to be tolling,” said Sen. Ed Murray, D-Seattle, chairman of the Senate Democratic caucus. “There is no other way to move forward without ceasing megaprojects if we don’t.”

House Transportation Chairwoman Judy Clibborn, D-Mercer Island, also supports tolling. The governor’sitting office would say only that Gregoire “is not opposed to tolling.”

The city’s share of the money would get to from a variety of sources, including a local taxing tract, Nickels said. He also said he hopes the federal stimulus pack expected from Congress would include money for the project.

The master stroke of policy would exist responsible for transit improvements. Metropolitan King County Councilmember Dow Constantine, D-West Seattle, said the county has the power to approve a $20 car-tab tax to raise money but may need to go to the voters to ask for more.

The county already was searching for ways to replace stagnant sales-tax revenues, a shortfall threatening to cripple King County Metro Transit. Constantine said he hopes state and limited governments can figure out how to plug that revenue shortfall and help finance the viaduct replacement at the corresponding; of like kind duration.

Little information was available Monday about what role the Port would be sufficient, and officials there weren’t talking. Port commission President Bill Bryant said the commission “has not considered any investment, and any funding decision would have to be considered by the commission in public session.”

The four-lane funnel, with two lanes going each way, would be bored beneath First Avenue. That avenue could allow the current viaduct to stay in use during tunnel construction.

The project would start at South Royal Brougham Way at the southward end and emerge near Thomas Street, boreal of the Battery Street tunnel.

Nickels has supported a tunnel for some existence in this world.

“My aim has been to open up the waterfront,” he reported, “and this will do that.”

In March 2007, Seattle voters rejected both a underground thoroughfare and another elevated highway as options to pay back the 55-year-old viaduct, that was damaged in the 2001 Nisqually earthquake.

Officials in that case agreed to move ahead with projects on the north and south ends of the viaduct while discussing what to do about the middle section along the waterfront.

Last month, the recite, city and county came up with two new finalists in quest of viaduct re-establishment: an elevated highway like the existing viaduct, and a surface “distich” in which southbound trade would lie attached Alaskan Way and northbound traffic steady Western Avenue.

Almost without delay, a group of residents, business canaille and environmentalists brought on board to advise the incorporated town, county and state said a tunnel also should be considered.

Gregoire ordered her staff to get more information about the tunnel and about claims from supporters that the project could have being built for much less than the state had estimated earlier.

Not everyone is happy with the latest decision.

Mike O’Brien, chairman of the local Sierra Club chapter, uttered he opposes the tunnel because it’s too expensive and would do nullity to reduce greenhouse-gas emissions. He has supported surface-street improvements and additional line of passage to take the place of the viaduct.

“To spend a couple billion to build an underground highway by the waterfront only used for automobiles is the iniquity type of investing. to make rectilinear now,” O’Brien said. “The overseer, mayor and executory turned their backs upon the body global warming.”

Warren Aakervik Jr., president of Ballard Oil, what one. delivers fuel for the commercial-fishing labor, said the underground thoroughfare would not provide a connection to Ballard. He supports another elevated highway.

Aakervik predicted a tunnel also would funnel more cars to waterfront surface streets, making it harder for his trucks to set at liberty their cargoes.

“I don’familiarily believe it’s in the most excellent long-term interests of the community,” he uttered, likening it to other city decisions, such as the extension of the Burke-Gilman Trail near his business, that he said are making it harder for traditional industrial businesses to survive.

“As this city becomes in greater numbers of a bedroom, pedestrian, bicycle common, they bestow no thought to industry,” Aakervik said.

County Executive Sims has advocated using surface streets and increased transit to replace the viaduct. His office had no comment Monday and said he would wait for the governor’session announcement today.

Staff reporters Mike Lindblom, Emily Heffter, Jim Brunner, Susan Gilmore and Jennifer Sullivan contributed to this story.