In an effort to preserve the quality of water at the Occoquan Reservoir, Fairfax and Prince William counties are being asked to adopt ordinances restricting recreational activities there.

The Fairfax County Water Authority, which owns the 1,700-acre reservior, has asked the two counties to adopt four measures curtailing swimming, fishing and some boating.

"These are preventive-type measures, not something that would amount to a loss of recreational privileges which now exist," said Water Authority spokesman Jim Warfield. "There's not immediate threat. It's just that we're concerned about the gradual deterioration which could occur as the population grows, and we want to maintain the status quo by not increasing the types of recreation allowed."

The proposed ordinances would prohibit:

Swimming.

Any boat powered by an internal combustion engine in excess of 10 horsepower.

Motorboats between Occoquan Dam and Fountainhead Regional Park.

Boating and fishing within 2,000 feet of the dam, excluding a 100-foot channel along the Prince William river bank to allow access to the reservoir from Hooes Run.

The proposal would exempt boats operated by the water authority or other governmental agencies.

The proposed ordinances, which have the backing of the Virginia State Health Department, would require approval by the boards of supervisors in both counties. No hearing dates have been set.

The two counties are expected to decide which agency will be in charge of enforcement. At present, Warfield said, boaters going into dangerous waters or swimmers were simply asked to leave if water authority personnel saw them.

Swimming traditionally has been banned at the reservoir for health and safety reasons.

"With swimming you get picnics and bottles and other debris people bring with them," Warfield said. "But a key concern is the safety issue. Every year we have a number of accidents and some people drown."

Kathleen Seefeldt, chairman of the Prince William Board of Supervisors, also cited safety factors in endorsing the proposed ordinance.

"There are no lifeguards there and no public beach as such," said Seefeldt, who represents the Occoquan District, where the reservoir is located. "We seldom get through the summer without a tragic death in the reservoir."

Seefeldt added that the proposal, suggested by some Prince William residents almost two years ago, is needed to "preserve the integrity of the water quality for the long run."