The Fairfax County Board of Supervisors voiced unanimous opposition yesterday to Federal Aviation Administration proposals that would distribute more evenly the noise made by planes taking off from National Airport.

The FAA suggestions would reduce the noise impact on communities along the Potomac River by creating alternate flight corridors over the Potomac that is now use. The supervisors object to the proposed flight changes because a significant portion of Fairfax in jet noise if the new routes increase in jet noise if the routes are implemented.

In rejecting the FAA proposal the supervisors not only endorsed the flight routs now in use at National Airport, but also requested that the FAA order planes to fly even further south and north than they do now before they turn over densely populated areas to heard toward their destinations. The supervisors want arriving planes to enter the Potamac corridoe sooner and departing aircraft to leave it later so that the noise over Fairfax County is minimized.

Now, pilots are supposed to fly north along the Potamac for about 10 miles to the point where the Beltway crosses the river at Cabin John Bridge or south of where the Woodrow Wilson Bridge carries the Beltway over the Potamac, according to John H. Thillmann, chief of the country's environment and technical services branch.

Supervisor Joseph Alexander (D-lee) suggested that planes fly south for at least 10 miles (to the Ft. Belvoir area) before turning. Supervisor John P. Shacochis (R-Dranesville) asked that the Great Falls area henceforth be the turning point on the northern route. Both suggestions were endorsed by the board.

In other matters the Board created an energy conservation task force to study long-range energy conservation for the county. William Morrill, special assistant to White House energy chief James Schlesinger, will serve as adviser to the task force, which will include representatives from various citizens' groups.

The Board also formally adopted a budget for the fiscal year that starts July 1 that calls for spending $496.2 million. Schacochis voted against the budget because he favors a tax rate cut that the supervisors earlier rejected.