SEATTLE – Gov. Chris Gregoire has given Seattle officials an ultimatum on a replacement for the decrepit Alaskan Way viaduct: No vote, no tunnel.

Unless city residents are able to vote before the end of the legislative session on April 22 about what to do with the 2.2-mile section of Highway 99, “it’s over,” Gregoire said Thursday, “because then I will instruct the (state) Department of Transportation to move forward with” a replacement viaduct.

The 53-year-old two-tier structure, a vital waterfront artery and a north-south traffic alternative to I-5, was damaged in the Nisqually earthquake in early 2001, and engineers say it might not survive another major quake.

In local squabbling over one of the state’s biggest transportation projects, Mayor Greg Nickels has argued strenuously for a $4.6 billion tunnel, others have favored a teardown and construction of a new $2.8 billion elevated highway, and some maintain that the existing viaduct can be less expensively stabilized and refurbished.

Further complicating the decision-making gridlock, some City Council members oppose a nonbinding, advisory election.

Last month Gregoire proposed a vote to break the stalemate.

Aides to the governor later drafted a letter to the city.

Her ultimatum Thursday caught Deputy Mayor Tim Ceis and council members by surprise.

“That’s not something she’d said to us that directly before, not at all,” Ceis said. “It doesn’t change the mayor’s political equation because he has said he is proposing this to be put on the ballot. We’re already taking all the steps necessary to get that under way.”

On Thursday, Gregoire said she thought her position was already clear.

Ceis said city and King County officials were discussing a vote on March 13 or April 23. A decision is needed by Jan. 19 to get ballots ready for March 13.

Jan Drago, a leading election opponent and head of the council’s transportation committee, said she was working to develop a compromise that would satisfy the governor without submitting the issue to a vote.

Council President Nick Licata said he couldn’t see what Drago could do to “make all sides happy.”