A proposal by politically powerful Fairfax County builders to take over certain building site inspections currently done by county employes has riled some local politicians, who say the move could leave new homeowners to pay for substandard sidewalks, gutters and drains.

The proposal, scheduled to come before the county board of supervisors today, is backed by county staffers, who say the current county building boom and a recent change in state law threaten to swamp already overworked county inspectors.

But some county supervisors say that allowing builders to hire their own engineers to inspect public utilities in new subdivisions increases the likelihood of shoddy inspection work.

"It's like asking the fox to mind the chicken coop," said county board vice chairman Martha V. Pennino, a Democrat.

"When builders get into a squeeze, they start cutting corners on public utilities," said Audrey Moore, a Democrat who has built her political career on opposing growth loudly and often. "Once we turn over this function to the builders we'll never get it back."

Board chairman John F. Herrity, who said he may support the proposal on an experimental basis, called Moore's fears that the county would lose control of the program permanently "patently ridiculous."

The debate over the proposal is sharpened by a new state law, effective July 1, that allows developers to request bond reductions as often as three times each year.

Under current state law, developers may ask for a bond reduction just once during the life of a construction project, and if county inspectors find that a substantial portion of the project has been completed, then the reduction is granted. The bonds guarantee that the county will be reimbursed for any portion of a project the developer cannot finish in case of default.

County officials say they fear that the new provision will mean a wave of new inspection requests.

"We normally get about 150 requests for bond reductions a year," said Claude G. Cooper, the county's director of environmental management. "With the new law, we're expecting 4,000 to 5,000 a year."

Cooper said the county would have to hire 21 employes to keep up with the anticipated crunch in requests for inspections. Fairfax now has about 1,600 bonded construction projects under way.

Cooper added that even if builders were allowed to hire their own engineers to do public utility inspections, county inspectors still would review the work through spot checks.

Most other area jurisdictions, including Montgomery and Arlington counties, use their own inspectors.

Moore, Pennino and other board members who are wary of a move away from county-administered inspections say the proposed change in policy could give rise to cozy relationships between builders and the engineers they hire to inspect their projects.

"It's pretty difficult for the engineer to bite the hand that's feeding you," said Pennino.

However, Supervisor Nancy K. Falck, a Republican who favors the change, said she doubts engineers will compromise standards to please builders. "They're putting their professional reputations on the line," she said.

Moore warned that the proposed inspection system would increase the number of unfinished or poorly built utilities and that homebuyers would be left to pick up the bill.

Supervisors who oppose the policy change say they favor either hiring additional county inspectors or having the county -- rather than the builders -- hire outside engineering firms.

Falck also said she opposed hiring additional county staffers, warning that they would be idle when inspections slow in the winter.

Supervisors say they expect a close vote when the question comes before the nine-member county board today.