The largest union of Sonoma County government workers on Monday soundly rejected a proposed contract that would have cut their pensions and pay.

Eighty-three percent of those workers, represented by Service Employees International Local 1021, who voted opposed the proposal.

About 1,200 of the 1,700 workers who would have been covered under the three-year agreement were eligible to vote. Voting began last Tuesday. The union represents about half of the county's 3,400 workers.

Lathe Gill, area director for Local 1021, said the proposed contact "didn't deliver enough on health care."

He also cited cuts to holiday time and pensions for the sweeping rejection.

"You can't live in Sonoma County for six years without a cost-of-living adjustment," Gill said.

The result canceled today's scheduled ratification vote on the proposal by the county Board of Supervisors and stalled the county's progress on long-sought measures to curb rising public pension costs and reduce overall compensation levels by 3 percent.

"It's disappointing," Supervisor Shirlee Zane said. "There has been a lot of work on both sides. We did have a tentative agreement, and we were hoping they would ratify it."

County Administrator Veronica Ferguson stopped short of calling the union vote a setback but acknowledged it delays changes county officials believe are necessary to sustain the pension system.

The proposed contract resulted from seven months of negotiations and was the first for the county's 11 bargaining groups to include both county-proposed and state-mandated changes to pensions, revisions that affect current and future employees.

The two sides are set to return to the bargaining table Wednesday.

"The county is going to continue to negotiate hard around the goals of reducing our pension costs and the total cost of compensation while trying to respect our workforce," Ferguson said. "The particulars of this deal being rejected does not change that direction."

The union represents mostly the county's lower paid line staff. Those workers have taken aim at the higher pay and perks of managers and argued that their own ranks have been unequally thinned in budget cuts from 2008 to 2011. They also have gone without a cost-of-living adjustment to their wages since 2007, a freeze that would have continued under the new contract.

Bargaining team member Tim Tuscany, a psychiatric nurse with the county's behavioral health division, said the proposed benefit reductions were unmanageable for the lowest-paid workers.

"The cost of our health care has become so high they can't afford it," Tuscany said.

A pair of lump-sum cash payments this year and next, totaling $2,200, plus increased county contributions toward employee medical costs apparently were not enough to sway union members.

"There is no guarantee they can get anything better, but they're willing to try again," Tuscany said.

On the concession side, a central provision of the contract would have shifted an additional share of pension premiums, equivalent to 2.25 percent of pay, onto employees.

New employees also would have been shifted into a new, lower tier of pension benefits expected to cost taxpayers less over the long term.

The vote is likely to affect talks under way with eight other county bargaining groups.

If the county-SEIU negotiations are not successful, the talks will have to go to mediation and fact-finding by a third party before the county could impose a one-year contract.