OLYMPIA — State Auditor Brian Sonntag said Monday he’s ready to close the books on his long political career and will retire when his term ends next year.

Sonntag, 59, called it a “tough decision” to not seek re-election in 2012 to an office he’s led for two decades, and made far more promin

ent and powerful than any of his predecessors.

He said he’s in good health, enjoys campaigning and isn’t bored in an office he’s served in since winning the nonpartisan post in 1992.

“It’s the 20-year thing. I’ve been thinking about how long is too long and how long is the right length of time to serve,” he said.

Sonntag’s put his stamp on a department long known for its steady churn of audits of taxing bodies: cities, counties, schools and special districts.

In the past decade he began measuring how well state agencies spend tax dollars using what are known as performance audits. These reports turned up the heat on practices of the state’s largest agencies including the Department of Social and Health Services and Washington State Ferries.

Voters in 2005 emboldened his efforts by passing Initiative 900 to lock in millions of sales tax dollars each year to produce the reports. They wanted the pot of money to give Sonntag fiscal autonomy from the Legislature. Instead, it has sparked clashes between him and lawmakers seeking to siphon some of the voter-earmarked dollars to help balance the budget.

“Founders of this state wanted the auditor to be a very populist, citizen-centric type of office and we’ve tried to make it that,” he said. “Because we did raise the visibility and credibility of the office, it created the environment for the performance initiative to happen.”

Monday’s announcement caught many off-guard as Sonntag has not talked about retiring. Earlier this year he even mulled a run for governor in 2012.

“I didn’t see it coming,” said Tim Eyman of Mukilteo, who wrote the 2005 initiative and been one of Sonntag’s loudest public allies.

“Very surprised to hear that Sonntag is moving on — he was in the unique position of being able to serve as state auditor for life,” said Jason Mercier, director of the Center for Government Reform of the Washington Policy Center.

Both Eyman and Mercier praised Sonntag for giving taxpayers a clearer sightline into how departments operate with the performance audits.

“He was kind of the Rosa Parks of performance audits. He was the first to sit on the bus,” Eyman said. “He’s laid the ground work for the program. I think the next auditor should take it to the next level.

Sonntag won his first election at age 26 when he became Pierce County clerk. He served two terms as the county’s elected auditor before capturing the post of state auditor with a slim majority in 1992.

He’s become one of the most popular statewide officials, topping 60 percent in his 2004 and 2008 re-election victories. As of Monday, no one had filed to run for the seat in 2012 because it was assumed he would run again.

Looking to the future, he didn’t absolutely rule out vying for another office somewhere, though nothing is in the works.

“I don’t know what the next chapter is going to be,” he said. “I don’t plan to retire into a rocking chair.”

Jerry Cornfield: 360-352-8623; jcornfield@heraldnet.com.