To the confusion of the American homebuyer and bewilderment of the homebuilder, everyone concerned with energy conservation in housing - federal and state agencies, product manufacturers and trade associations - have been making recommendations and writing standards to cut energy use.

Many do not agree with one another. Some state-wide requirements do not make adjustments for significant climate variations within the state.

Others prescribe single systems without recognizing equally effective alternates.

And none to date have considered the question of cost to either the builder or the buyer. As one research-oriented homebuilder put it recently, "I can build a house that would cost practically nothing to heat or cool, but no one could afford to buy it."

Now, to bring order out of this chaos, the National Association of Homebuilders has issued its thermal performance guidelines for one and two-family dwellings.

Unlike other proposals, the NAHB guidelines take into consideration local variances in climate and fuel costs. With this approach, a spokesman for the NAHB Research Foundation says, "We'll give the homebuyer a bigger bang for his buck. If he invests an extra dollar for energy conservation, he can be sure that he will get it back within several years." The seven-year payback period is considered desirable because this is the average length of time American families occupy single houses.

The heart of the thermal performance guidelines is a formual for establishing an energy index for any locale in the U.S. The formula requires the filling out of a form similar to an IRS tax return. It includes data on winter degree days, summer cooling hours, costs for fuel and electricity.

The builders organization has compiled data on average winter degree days and summer cooling hours for 150 three-digit zip code areas to guide local applications. Soon, it expects to expand the list to more than 400 areas. All the local builder must do is add the local price of fuel and electricity to determine which system will provide the best investment.

Determining the best energy conservation technique is simplified by the use of scaled bar charts for 19 different construction systems: wood frame walls, brick masonry walls, ceilings, etc.

For instance, the energy index for a house in the Washington area using heat and electric air conditions suggests that the best calling insulation investment would be R-19, six inches of mineral wool blanket insulation or its equal. However, if the basic heating fuel was oil, which costs more in this area, the energy index would be higher and R-30 would be recommended as the best investment for ceiling insulation.

In the gas vs. fuel oil example, the variance is not as great for side walls. In wood frame construction, a gas-heated house should have R-12, compared to R-14 for an oil-heated house. The index indicates that both should have double glazing on windows and patio doors. But, storm doors are a poor investment, especially when used with solid wood or insulated doors.

The cost effectiveness of the various construction systems is based on several assumptions, combined to create what the NAHB calls "present worth factor."

The basic assumption is that energy costs will rise an average of 10 per cent per year for at least the next seven years. Other assumptions are variable, such as interest rates and desired pay-back time.

For instance, paying 9 per cent interest, a homeowner who wanted a seven-year payback on his energy savings investment would spend $7 today to assure a $1 saving the first year - and a complete return by the seventh year.

However, if energy costs started rising by an average of 15 per cent a year, he could afford to spend $8.72 to assure a full return at the end of seven years.

Some measures suggested by the study:

Reduce air infiltration to the minimum by weatherstripping windows and doors and caulking cracks around all openings and the joints between the house and its foundation. Because the labor required is the same, use high grade materials. In caulking this would mean high-performance polysulfide, polyurethane or silicone.

Pay careful attention to insulation installation, making sure that the batts or blankets are fully butted and stapled in place. Areas above doors and windows, and below windows should be fully covered as well as areas behand electric boxes and piping. Vapor barriers should be placed to face the heated side of the house.

Clock thermostats should be installed. Dollar for dollar they offer the quickest return on investment - often paying for themselves in the first year.

Water heaters, the second largest users of energy in most households, should be set at about 125 degrees and left alone. These heaters should be located as close as possible to the areas of greatest use - bath and laundry rooms - to avoid heat dissipation in the pipes.

Pick heating and cooling equipment and appliances with the highest energy efficiency ratings. Ratings of 6 and 7 used to be typical but newer equipment is coming on the market with ratings of 8 and 9. The higher, the better. However, avoid over-sized equipment. It is less efficient and costs more.

Ductwork should use the shortest possible runs with the fewest possible turns. All joints should be taped and exposed ducting should be insulated, Like clock thermostats, insulated ducts pay off fast.

House shapes such as squares and rectangles have less exterior wall space in relation to floor space than L-, T-, or H-shaped houses and use less energy.

Fireplaces should have tight fitting dampers, glass doors and outside air supplies to the fire-box. Heat recovery and air recirculation devices should also be considered for traditional type fireplaces.

Make sure there is adequate ventilation of the attic to avoid winter condensation and lower summer temperature.