In his "fireside chat" last week, President Carter appeared to set a less than perfect example for energy-conscious Americans: he had the White House thermostat turned down to 65 degrees, but the crackling fire he sat in front of is a possible energy waster.

Lowering thermostats has long been urged by energy authorities as a key to fuel conservation. For each one-degree dip in a thermostat's setting, fuel costs are said to drop by 2 to 5 per cent.

But among an outpouring of energy-conserving tips spawned by this frigid winter's fuel crisis have been repeated warnings about the old-fashioned fireplace.

"Don't use your fireplace for supplemental heating," the Federal Energy Administration cautions in one of its energy-saving reminders for February. "More room neat probably will be lost up the fuel than you get from the fire."

Fireplaces and thermostats are among dozens of devices renewed examination by government and private engineers, consumer groups and home owners as fuel costs mount and emergency measures spread to contend with the nation's latest energy crunch.

There are scientific studies and public-minded appeals, commonplace advice and newly designed gadgets, general agreement over the merits of conservation and some disagreement over what steps an ordinary American might take to economize on energy.

The discussions range from attic insulation to dripping faucets, from leaky air ducts to keeping an oven door shut, from insulated jackets for water heaters to closing draperies in front of windows at night. Almost every room of a house or apartment is being probed by energy specialists who are seeking ways to maintain warmth with less fuel.

President Carter himself has sought to stir efforts by home owners and apartment dwellers to use the nation's dwindling oil, gas and electricity supplies more sparingly.

"All of us must learn to waste less energy," Carter said in his fireside talk last Wednesday, as he sat in the chilly White House library. He wore a cardigan.

"Simply by keeping our thermostats at 65 degrees in the daytime and 55 degrees at night we could save half the current shortage of natural gas," he added. "There is no way that I, or anyone else in the government, can solve our energy problems if you are not willing to help."

According to Carter's media adviser, Barry Jagoda, the White House never considered whether an old-fashioned fire conserves or wastes energy during preparations for Carter's televised talk.

"The purpose of having a fire in the fireplace was because it was chilly in the White House," Jagoda said. The burning logs, Jogoda added, conveyed a sense of intimacy and homey warmth and also provided, a natural setting for the president's talk since Carter normally has fires blazing in the White House on cold days.

While the Federal Energy Administration and other government agencies have a recently cautioned against home fires, none criticized the President. Asked whether Carter was setting a good or bad example by sitting beside the burning logs an FEA engineer replied, "I'd hate to be quoted as giving you an answer."

Carter's 65-degree recommendation marks the lowest proposed setting for American thermostats in recent years - lower than that suggested during the Arab oil embargo and a symptom of deepening concern over fuel shortages.

Attitudes toward home insulation have undergone a similar shift, with some energy specialists recommending thickers layers of cold weather buffers than they did a few years ago.

The Consumers Union says it is searching for new fuel-saying techniques for home owners and will publish a series of reports on its findings in its magazine, Consumer Reports.

Ryan Homes, Inc., one of the nation's major home builders, is trying to promote sales by offering increased insulation and other energy-saving devices. The firm says it is using a $45,000 electronic camera to check for heat leaks in its buildings.

The Energy Research and Development Administration drew almost 300 industry and government energy specialists to a meeting this week to discuss ways of spending $3 million in ERDA funds this year to help design new equipment to cut fact consumption.ERDA officials say the research program has already led to production of insulated water heater jackets. They are now encouraging study of such concepts as heating water with the same heat that has been removed by a refrigerator.

Amid the flurry of scientific study and unscientific exhortation has emerged a variety of energy-conserving recommendations by government agencies, utilities and other organizations, ranging from lowering thermostats and adding insulation to closing the damper in the fireplace. Insulation

Most houses in the Washington area and across the United States are said to have insufficient insulation, especially in their attics. They were built during an era of cheaper fuel when home builders and buyers showed less concern for energy saving, government and private energy specialists say.

Although agencies in the Washington area differ over how much insulation a home owner should install, they appear to agree that some insulation is essential. The Federal Energy Administration says that installing attic insulation will likely cut heating costs by 20 per cent.

The effectiveness of home insulation is now measured by its R-value, or resistance to heat penetration. Insulation is available in rolls and flat strips, or batts, of figerglass, asbestos and other materials. It may also be obtained in loose, or granulated fill, such as vermiculite. Each material carries it sown R-value.

A newly issued study by an economist for the National Bureau of Standards recommends that gas- and oil-heated homes in the Washington area have R-30 insulation in their attics, R-14 in exterior walls and R-11 under floors located above unheated areas.For homes with electric heating, the study suggests R-38 for attics, R-14 for exterior walls and R-19 beneath floor over unheated areas.

R-30 is equivalent to the rating of a 10-inch thickness of a fiberglass batt of blanket. R-38 would require 12 inches of the same material.

The National Bureau of Standards publication, which offers tables and formulas for computing costs and savings of installing insulation and carrying out other fuel conservation techniques, is available for 70 cents from Consumer Information, Pueblo, Colo., 81009. Its title is, "Making the Most of Your Energy Dollars in Home Heating and Cooling."

Arthur W. Johnson, energy conservation director for the NAHB Research Foundation, a subsidiary of the National Association of Home Builders, differs with the National Bureau of Standards over some of its suggestions, describing them as "rather exorbitant."

Johnson himself recommends that Washington home owners who have no insulation in their attics put down 6-inch thicknesses of batts or blankets, with vapor barriers at the bottom. If they already have up to 4 inches of attic insulation, Johnson says, they should lay on an additional 3 1/2 inches, without vapor barriers.

Installing insulation in an attic in which there is none may save close to $200 in fuel costs a year, Johnson said. Adding insulation on top of an existing layer brings much smaller savings, only $20 to $30 annually, Johnson noted.

The Washington Gas Light Co, recommends R-30 insulation in attics and R-14 in walls. The Potomac Electric Power Co. suggest a minimum of R-19 in attics and R-11 in exterior walls and floors above unheated areas.

Some insulation can be installed by home owners themselves, such as that in unfinished attics. Government and private agencies caution that protective face masks, gloves and long sleeves should be worn, especially when handling asbestos or fiberglass. Installing insulation in exterior walls, by such techniques as mechanically blowing in loose fill, normally requires a professional firm, energy specialists say. Water Heaters

Heating water accounts for about 15 per cent of the energy used in American homes, according to FEA. Government and private agencies recommend a series of steps to keep water heaters operating efficiently.

They urge that the temperatures setting of a home water heater be kept between 120 and 140 degrees.Temperatures exceeding 140 degrees are described as wasteful, and a 120-degree setting is said to be sufficient for homes without dishwashing machines. Washington Gas Light Co. suggests setting dials at the "pilot" position when a family is away from home for a week or more.

Periodically energy specialists say, a gallon or so of water should be drained from the bottom of a water heater to remove sediment. Otherwise, they say, the sediment acts as an insulator between the water and the heating element and leads to increase use of gas or electricity. Some recommend draining sediment once a year; others say several times a year.

Energy agencies and utilities caution home owners not to install larger water heaters than they clearly need. An unnecessarily large water heater uses an excessive amount of fuel, they note.

Government and private energy specialists urge that steps be taken to insulate water heaters and hot-water pipes as well. Insulation sleeves are available to fit water pipes of varying dimensions. Several new kits have been produced for insulating water heaters.

Consumer Reports magazine described its own testing of water-heater insulation jackets last month. It reported possible fuel savings of $10 a year for gas heaters and $25 annually for electric heaters. The insulating kits are sold for about $20 each. Thermostats

Most energy authorities appear to be falling in line with President Carter's recommendation that thermostats be lowered to 65 degrees in the daytime and 55 degrees at night. They suggest that the lower setting be maintained during periods when families are away from home.

To help regulate day and night settings for home thermostats, several devices are available, energy specialists note. These include clock thermostats, which automatically set temperatures lower at night, and some less expensive gadgets, costing from $10 to $30, that may have the same effect. By heating air near the thermostat, these devices trick the thermostat into acting as though the air throughout the house is warmer than it actually is.

Some authorities also suggest installing humidifiers in homes on the theory that adequate moisture makes cooler air feel more comfortable. An inexpensive substitute, they say, is a pan of water placed on a radiator.

As another step to regulate home temperatures, energy officials recommend closing off rooms that are not in use and shutting off radiators and heating vents in these rooms. Heating Systems

Furnaces and other links in a heating system require regular maintenance, energy authorities say. Furnaces should be cleaned and adjusted annually by professional service people, they say. A home owner should check air filters frequently and replace them when they are dirty.

Heating ducts should be insulated and examined for air leaks, especially at the joints, fuel specialists say. A leak can be repaired with adhesive tape or special duct tape. The FEA recommends that radiator surfaces be dusted or vacuumed often and suggests placing sheets of aluminum foil on walls behind radiators to reflect heat into a room.

Many energy authorities, including Pepco officials, say that a heat pump is a less costly heating system than a standard electric furnace.

For fossil-fuel furnaces, several new devices are being sold that are designed to recapture heat that would otherwise go up the fuel. Among them are heat exchangers installed ina fuel pipe that intercept waste heat as it rises toward the chimney. Windows, Doors

Drafts through cracks around windows and doors may account for 15 to 30 per cent of a family's heating bill, government officials say. One remedy is caulking and weatherstripping around windows and door frames.

In the Washington area, according to the National Bureau of Standards, home owners will find it economical to install storm windows outside all windows that are 9 square feet or larger. Storm windows and doors are said to cut heat losses through regular windows and doors by 50 per cent.

A cheaper substitute, many officials note, is transparent plastic sheeting or a specially fitted sash that may be attached outside a window. The aim is to create a dead air space that acts as insulation.

Energy agencies note that draperies, blinds and shades should be drawn at night to provide further insulation, but they should be opened when the sun is shining because sunlight helps heat a house. Shrubs and Trees

Shrubbery, some government officials say, may be planted near a house to block wind and help insulate the building, especially on the east, west and north exposures. Deciduous trees, they add, let sunlight in during the winter when their leaves have fallen, and provide shade during summer. Kitchens

Tips abound for energy conservation in the kitchen. According to government agencies and utilities, they include:

Use glass or ceramic dishes, rather than metal pans, in the oven. The oven temperature may then be set about 25 degrees lower.

Never boil water in an open pot, and turn down the heat to simmer once the water comes to a boil.

Pressure cookers and microwave ovens speed cooking and save energy.

Only run a dishwasher when it is full. Shut it off after its final rinse, allowing dishes to air dry.

Only preheat an oven when necessary for baking or broiling. Never preheat it for more than 10 minutes.

Repair leaking hot water faucets quickly to save hot water. By some estimates, an average drip may waste between 650 and 3,280 gallons of water a year.

Avoid opening an oven door whenever possible. Each opening is said to result in a 20 per cent loss of heat. Laundry

Similar energy-saving suggestions. Have been made by government and private agencies for using washers and dryers. These include presoaking heavily soiled clothes and using cold or warm, rather than hot, water settings whenever possible. Installing an exhaust vent to the outdoors is said to reduce running time for a dryer and to save energy. Running a washer or dryer only with a full load of clothes and keeping a dryer's lint filter clean are also among often repeated energy-savings tips. Bathrooms

Showers appear to be the chief energy-saving issue in the bathroom.

"Take more showers than tub baths," says the Federal Energy Administration "Showers use less hot water, hence less energy than tub baths."

"Try taking shorter and/or not-quite-so-hot showers," says the American Gas Association.

"And perhaps, you don't need to take a shower every day," says the National Association of Home Builders.

Another energy-saving suggestion for the bathroom is to fill the basin partly with hot water when shaving rather than letting the hot water faucet run. "You'll shave dollars from your gas bill and water bill," the American Gas Association says. Fireplaces

Most fireplaces draw heat from a house and send it wastefully up the chimney, according to some government and private energy authorities. "The fireplace can be a net loser of energy," said John Muller, an engineer for the Federal Energy Administration.

An additional drawback, these officials note, is that dampers are often left open after a fire has gone out, allowing still more warm air to escape.

Yet fireplaces apparently still have some virtues. In fall or spring when a home furnace is not in use, a fire in the hearth may help lessen the chill indoors, without wasting energy, officials say.

Even in winter, it is said, a fireplace may be used efficiently to heat a living room. But the rooms' doors should be closed and a window opened slightly, energy specialists add, so that heat will not be drawn up the chimney from other rooms in the house. Or, they note, a family might instead shut off its furnace when burning wood in the fireplace. A fireplace is also useful to have, officials say, as a safeguard against a heating breakdown or emergency fuel cutoff.

A number of devices may be purchased to help prevent heat from escaping up the chimney when a fire is blazing. Among them are glass screens that restrict the flow of heat from a room to the hearth, special duct systems that distribute air warmed by the fire back into the room, and heat exchangers that recapture lost heat on its way up the chimney.