A Fairfax County advisory committee recommended yesterday that county supervisors limit any increase in real estate tax bills to 5 percent a year or less.

Assuming that the cost-of-living continues to rise, Acting County Executive J. Hamilton Lambert warned that the tax rate would have to be reduced each year to meet the committee's recommendation.

County officials said it would be virtually impossible to limit the real estate tax bill increases to 5 percent or less, as long as the cost of running the county continues to rise as it has in recent years.

The county supervisors reduced the real estate tax rate last year and are expected to reduce the rate again this year, but most property tax bills will continue to grow because of rising assessments.

The citizens' committee was created last year after California voters approved the tax-cutting Proposition 13. Yesterday it presented its recommendations to the supervisors in a thick report.

The committee also recommended that the county staff review some of the "autonomous" agencies within the county bureaucracy to determine if they should be directly accountable to the county executives.

Among those agencies suggested for study were the county park authority, the water authority, the stream valley board and the county's criminal justice coordinating council.

"To say, we are an autonomous organization is wrong." said Joseph Downs, director of the park authority. "Our budget is approved by the county [supervisors]. The authority members are appointed by the county supervisors. Our employes are merit employes... We are not free to do whatever we please."

The committee also recommended that some agencies and commissions, such as the Tree Commission, to be reviewed to determine if they are needed. Vernon Walker, chairman of the Tree Commission, said, "I guess it boils down to if trees are important to the environment."

The supervisors referred the report to the county staff for comment.