Energy conservation is being preached high and low in Fairfax County.

In the county government's 12-story Massey Building tower, the lights are being turned off floor by floor as soon as the night workers empty the wastebaskets.

In the bolier rooms of about 35 public schools, some custodians will be replaced by engineers who know how to keep furnaces and air-conditioning systems on a low diet of power.

Energy conservation is a big topic in the board room of the governing supervisors. Martha V. Pennino (D-Centreville) got her colleagues to endorse a lettle she sent to federal energy czar James R. Schlesinger urging him to work for "a body of laws" that would give local jurisdictions like Fairfax the authority to impose a number of energy-conserving steps. Her proposals include mandatory energy-impact statements on all public and private construction.

Another supervisor, Alan H. Magazine (D-Mason) will ask his colleagues Monday to create a task force "to develop a long range energy conservation plan for the county government, the citizens and the private sector."

But amid all the preachments, Fairfax has been making zoning and other land use decisions that will dictate increasing reliance on the automobile, one of the major users of energy.

Under the count's relatively new development law, specifically its Planning and Land Use System (PLUS), more intense development within the Beltway was de-emphasized in favor of homes built on large lots throughout the western part of the county.

PLUS-type development is already proceeding at a pace that has flabbergasted many county officials. "You have to see it to believe it," School Supt. S. John Davis told a meeting of school-bond supporters the other day.

Scattered development in the far corners of the county puts workers and shoppers farther from employment and commercial centers. Because mass transit is uneconomical in spread-out suburbs, residents must rely almost exclusively on cars, driving many miles not only to get to their jobs but to buy a loaf of bread or carton of milk.

There are desirable alternatives, officials say, but some of them point out that the options are not politically realistic.

"I'm pretty well convinced one way to reduce energy consumption is to build higher densities closer in," says Supervisor Magazine, who represents a populous district in the eastern part of the county. "But I don't think higher density is acceptable to the citizens. And it's not acceptable to me because it's not acceptable to them."

Planning Commission Chairman Edward Gurski is even more candid about the dilemma. "What disturbs me is the way we live, the way I want to live. We each want a little white cottage on its own piece of ground."

Unit her district was realigned, Supervisor Pennino used to represent the communities of Greenbrier and Brookfield, often cited as classical examples of leap-frogging development. "They are beautiful suburban communities," she says. "But they are almost prohibitive in their energy consumption."

Yet more Greenbriers and Brookfields are being created under PLUS, which is a set of zoning laws and other measures to control how many homes can be build and where. Mrs. Pennino who in the past has defended PLUS as a comprenhensive plan that sought to maintain "the qualtiy of life" in Fairfax, now says: "Unfortunately PLUS is promoting energy consumption instead of conservation."

Mrs. Pennino dosen't think Fairfax could do any better in energy-conserving planning until the federal government commits itself to giving financial support to compact new communities that straddle major transportation corridors. But in recent years the government's aid program for new communities has come to a virtual halt because many of the developments, caught up in the housing recession, defaulted on HUD-guaranteed loans.

Though the automobile is a gluttonous consumer of fuel, Fairfax officials concede they don't know precisely how much energy county residents consume in driving.

According to Metropolitan Washington Council of Government figures from 1973 - the most recnet ones - Fairfax residents each use 30 per cent more fuel for transportation than the per capita usage by residents in the entire metropolitan area. This figure includes only trips within the county. Because about 60 per cent of all Fairfax workers drive to other jurisdictions, at often greater distances, fuel transportation consumption for transportation is probably even greater among Fairfax residents.

While Magazine says he is not ready to endorse any significant shifts in planning, he does think the energy task force he is proposing would "have to take another look at the PLUS plan's (low) densities."

Magazine's suggestions for study by task force include:

Requiring county staff to prepare energy impact statements on all construction proposed in rezoning applications - an idea similar to Mrs. Pennion's.

Examining the feasibility of basing fees for county vehicle tags on Environmental Protection Agency mileage ratings, charging less for more efficient cars. At present, the county charges $20 for cars weighing 4,000 pounds or less and $25 for cars weighing more.

Computerizing heating and cooling controls for the Massey Building and other county-operated offices. Magazine said that savings at the Massey Building alone could range from $30,000 to $120,000.

The state of Virginia already has begun to act in one area where Magazine proposed action - stiffer thermal requirements for new construction. The State Housing Board will hold public hearings this fall on revisions that have been recommended by the State Building Code Technical Review Board.

According to Noman M. Cole Jr., an energy adviser to gubernatorial candidate John N. Dalton, Virginai residences are 26 per cent less energy-efficient than the U.S. average. Cole said there are only minimal energy-efficiency requirements for new singlefamily homes and none for new multi-family or commercial construction.

Magazine said he was proposing his task force as a way of helping to meet Carter's goal of reducing oil and gasoline consumption by 10 per cent a year and reducing the growth of total energy consumption from the present 7 per cent rate to 2 per cent.

The Fairfax school system is considering a number of steps to reduce its energy consumption. One of the plans involves hiring engineers, instead Of custodians to take care of heating/cooling plants.Computerized controls, which can continuously adjust heating and cooling for maximum efficiency, are also being explored.

Another possibility, according to Supt. Davis, is to have high school students walk to neighboring elementary schools before they are picked up by buses.

Davis estimates that the use of 87 buses could be eliminated if 25 miles of sidewalks were built in neighborhoods near elementary schools, but such construction has usually been cut from county budgets in recent years.

Some ideas not only don't work - they backfire. Davis said the school system had been using reclaimed crankcase oil as a supplement to its heating fuel, but had to abandon the project because the salvaged oil was sending hazardous emissions of lead into the atmosphere.