When builder Leslie Lutor constructed his family house in the Manor Park area of Montgomery County, he was generous with the insulation, putting in 13 inches of fiber glass in the ceiling, for instance. That's twice as much as usual. After living in the house for more than a year, he has found that utility costs have averaged $133.72 a month, about 2 1/2 cents a square foot.

While many total utility bills range over $100 a month in this area, the average house size is less than 1,800 square feet. On a comparative basis, costs of heating and cooling in Lutor's 5,200-square-foot house are well below average for a house of that size.

A member of the energy staff of the research foundation of the National Association of Home Builders said that the utility cost figures are obviously below average. But he added that any residential energy-conservation analysis must be be carefully monitored, taking the life style of the occupants into consideration - noting how high and low thermostats are set in summer in winter, for instance.

Lutor said that his settings were "comfortably average in booth the heating and cooling seasons."

He added: 'I think the low costs of utilities justify the heavy insulation, the styrofoam under the slab, insulation around the windows and doors to make them air-tight and an efficient heating and air conditioning system."

The two-story brick house sits on a wooded half-acre lot on Norbeck Road. The house has a light brick exterior on the first level, complemented by a "double-wall" system on the upper level. The roof line was extended downward 7 feet and constructed in a way that creates dead air space between the exterior and interior wall. The upper exterior is covered with heavy asphalt shingles.

"We have a propane gas-fired system for back-up heating when the temperature goes below 32 degrees," said Lutor. The house also uses a an electric heat pump and electricity for all appliances.

A hungarian refugee trained in architecture and engineering who has been in this area for 17 years, Lutor formerly worked for architect Vlastimil Koubek and for developer-builder Carl M. Freeman.

Lutor has nearly completed a similar house next door, which he hopes to sell for $185,000. CAPTION: Picture 1, Builder Leslie Lutor. By Margaret Thomas - The Washington Post Picture 2, Utility costs for Lutor house on Norbeck Road average $134 a month. By Margaret Thomas - The Washington Post