From Pullman to Puyallup, gubernatorial candidate Jay Inslee has trumpeted prevention-based health care for state employees as a way to save hundreds of millions of dollars a year.

But now the Democrat has cut his cost-savings estimate by as much as two-thirds, raising new questions about the feasibility of his vow to boost education spending without raising taxes.

Campaign staffers insist the proposal would still generate significant savings. But some government officials, health-care experts and union leaders say that isn't clear without further study.

Inslee and his Republican opponent, Rob McKenna, agree that controlling health-care costs is crucial to adequately funding education without new taxes, as both have pledged.

McKenna wants to cap health-care spending and raise the share of premiums paid by employees unless they switch to a consumer-directed plan, which pairs higher deductibles with health-savings accounts. Persuading unions to accept those changes could be a challenge.

Inslee's plan would shift state employees to a health-care system similar to the one adopted in 2005 by King County, which lowered costs through wellness programs, greater use of generic drugs and other strategies. Inslee has said it could save between $300 million and $455 million a year if implemented statewide.

However, his campaign recently discovered that King County actually saved only a third of what Inslee has been saying on the campaign trail. Because the state savings estimates are based on the county's experience, the campaign has scaled back its numbers.

"If you want to argue that $200 million or $100 million in savings to the state is insignificant, I think everybody in the world would argue with you," said Sterling Clifford, a campaign spokesman. "Frankly, if it's $50 million, it'll be helpful."

State health officials also note they've already adopted parts of King County's system, would have trouble doing some other aspects of it and, of course, would have to negotiate changes with many labor unions.

"There are 100 moving parts in this type of discussion," said Lou McDermott, the director of the public-employees benefits division of the state Health Care Authority. "None of it is simple."

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Inslee scales back expected savings from a centerpiece of his platform