Fairfax County officials predicted yesterday that nearly two-thirds of its 11,000 employees would be rated "superior" or "exceptional" under a proposed merit-pay system, requiring the county to pay $10 million more in raises than it did last year.

Employees in the top two categories would get raises of 5 percent or 7 percent, officials said. About one-third of the employees would be rated "satisfactory" and receive a 3 percent raise, and 1 percent would be deemed "unsatisfactory" and get no raise, according to county estimates.

The information was greeted warmly by many county employees but caused others to wonder whether the new system--touted as a way to reward employees who work hard--would be too generous.

"I think pay for performance is the way to go. But I am very concerned about 65 percent of the work force being rated superior or exceptional," said Fairfax Board of Supervisors member Michael R. Frey (R-Sully). "I think it's going to be awfully expensive."

The new pay plan was part of a larger push by former county executive Robert J. O'Neill Jr. to reform the massive county bureaucracy. He argued that the county's workers needed to prove they deserved raises by performing well on a series of criteria. So-called cost-of-living raises, which are given automatically, should be phased out, he said.

O'Neill received support for that concept from employee groups last year. But the specifics are being criticized by those same groups, who say officials are rushing to implement it before making sure the evaluation of workers will be fair and unbiased. O'Neill left the county this month to head a government think tank.

Yesterday, officials gave details of how the plan might work and how much it might cost. Based on past evaluations of employees, they predicted that half of employees would be rated "superior" and 15 percent would get the top grade of "exceptional." Supervisors are considering the proposed pay plan as part of the county's overall budget, to be approved in April.

Virginia Stanton, head of the Employee Advisory Council, said her group opposes immediate adoption of the new pay plan because many county departments have not yet established specific criteria on which employees will be judged.

"I'm still getting calls from individuals saying their agency is frantically working on these performance elements, and they don't know what they are being judged on," Stanton said. "Our position is: Slow the process down."

Harish Patel, a 10-year county employee who is an accounts clerk, said he was worried that he might be hurt financially if the new policy went into effect. "I'm not too happy about it," he said. "I'm concerned about favoritism. It's not the policy but the execution that I'm concerned about."

Other employees had a different reaction. "I like it. I think it's good," said Cord Faulkner, who works in the county's finance department. "Obviously, the better you work, the more you should be paid."

Supervisor Penelope A. Gross (D-Mason), who chairs the board's Personnel Committee, said she wants further discussion of the concept next month before she would be comfortable voting to go ahead with the plan. "County employees feel that this is moving too fast and are not comfortable with it," Gross said. "The question is how you objectively evaluate somebody."

Gross and other supervisors will also have to decide whether they can afford the plan this year. Last year, raises for county employees totaled $24.7 million. With the new pay plan, officials estimate raises would cost $35.1 million.