The Fairfax County Board of Supervisors sharply attacked two bills before the Virginia legislature yesterday, one to loosen bonding requirements for developers and another to lift the statewide ban on uranium mining. The supervisors said both would create special problems for Northern Virginia.

Supervisors said the bonding bill would grant huge breaks for developers who cannot finish subdivisions and would leave taxpayers to pay for many improvements required by the county.

"This is nothing more than welfare for developers," said Supervisor Thomas M. Davis III (R-Mason). "It's an assault on local jurisdictions."

"This is a run by the special interests to take the right of the people to control their own destiny away from them," said Supervisor Audrey Moore (D-Annandale).

The piece of legislation that inspired their wrath is sponsored by Del. Ralph L. Axselle (D-Henrico) and is a nine-page revision of the laws governing how developers live up to their promises to complete projects. The bill is before a House of Delegates subcommittee.

It would revise state law by stopping counties from requiring bonding for completion of private streets, gutters, drainage systems and sidewalks, the county says.

The bill would also guarantee zoning for developers for five years after their preliminary building plans are set. The county says that would "lock in" zoning and would not allow it flexibility to impose more restrictive zoning when it wishes, as it did in the Occoquan Basin in 1981.

Builders, who have lined up in support of the bill, say that Fairfax' overly stringent bonding requirements are to blame for the county's rate of builder defaults, which has been among the highest in the country.

"The bill will reduce significantly the number of defaults in the county," said Samuel A. Finz, chief executive officer for the Northern Virginia Builders Association. "Builders will only bond what they can handle at a given time."

The board also attacked a bill that would lift the ban on uranium mining in Virginia. Fairfax County Board Chairman John F. Herrity, who sponsored a resolution opposing the bill, warned of "substantial risks" to the environment posed by possible uranium mining in Northern Virginia. The resolution was adopted without opposition, although Herrity, who suffered a heart attack two weeks ago, was not present at the meeting.

In a letter circulated to the board, Herrity charged that Marline Uranium Corp., a New York-based firm that ended its explorations in Northern Virginia in 1982, remains interested in mining uranium in the area.

A spokesman for Marline called Herrity's charges "absurd," declaring that the state's uranium deposits were in Pittsylvania County, in Southside Virginia.

In other action, the board last night approved an amendment to the county's comprehensive plan that would allow construction of an 1,800-unit residential development near the fast-growing intersection of Interstate Rte. 66 and Rte. 50.

The development, which now requires rezoning approval from the county planning commission and the board, would be located north of Rte. 50, directly across from Fair Oaks Mall, and would incorporate the existing 130-acre Penderbrook Golf Course.

The developers, Potomac Investment Associates, originally sought 2,400 units, including townhouses and low-rise multifamily buildings, but compromised with county officials to win approval for their plan.

The developers agreed to a plan that would preserve the golf course in return for high density development on some parts of the 322-acre site.

County officials said the rezoning application will probably come before the board early this spring, and that construction could start in 18 months to two years.