An earth-sheltered house with passive solar heating will be open to public inspection today and tomorrow at a sylvan site in the mountains northwest of Frederick, Md.

Built by the Frederick-based M.S. Milliner Construction, Inc. with the benefit of a $12,000 grant from the Department of Housing and Urban Development, the three-bedroom house was designed and built to conserve energy for heating and cooling inside its reinforced concrete block structure and also to capture sunshine for interior heating during the winter.

Exterior shades shield a front heat-collecting room in the summer, and the house remains comfortable in 90-degree weather by virtue of its tight envelope and contact with the earth below and in back and a 65 percent side cover. Only the front of the contemporary styled house is fully open. The exterior masonry is covered with a stucco material and painted white. A dark fir band trims the house.

Built on a 3.6-acre site in the Vista Farms subdivision in a rural area of Frederick County, the 2,700-square-foot Terra Vista house has a contemporary facade and is landscaped with a ring of tall trees that provide privacy and shelter.

Two years in the planning and building, the house is for sale for $144,800. Twenty-nine-year-old Mike Milliner heads the firm that built the house -- for which 300 pages of documentation were submitted to the Department of Housing and Urban Development.

At a preview showing earlier this week, Milliner told visitors that the house was dug only 7 1/2 feet into a small hill that slopes into the back of the house. Both roof areas of the two-story house are covered with 18 inches of sod on which wild flowers, grass and some weeds are growing.

A slanting window area distinguishes the front of the house and transmits solar rays through a new 3-M system of Weather Shield double glass with an invisible interior film that enhances solar transmission while also providing additional insulative value.

Inside the wide but narrow greenhouse room in front, a concrete floor and wall collect solar heat which is transferred by a convection system to other areas of the house.

After the exteriorf work was completed, Milliner said the interior temperature last winter was 55 to 60 degrees for workmen finishing the house, without any additional heat. However, the house has an electric heat pump system for what Milliner says is back-up heating and air conditioning and a wood stove in the center of the house.

A larger-than-usual chimney provides a vent for the stove and also an outlet for interior air circulation tied to a vent pipe that goes below ground to admit air that has been cooled below ground in summer and heated somewhat in winter.

Bob Toth, an assistant to Milliner in the construction business started eight years ago, compared the house with a large submarine with a view. Vertical windows across the top of the house front provide considerable light for the bedrooms, kitchen and dining room on the upper level of the house that has a living room, one bedroom, a garage and greenhouse on the first level.

Because the house was built under a HUD and Department of Energy demonstration program concentrating on passive solar applications, the objective was to produce a dwelling that would require a minimum of energy from conventional sources.Milliner estimated that less than a cord of wood burned in the Buckstove would make the house comfortable during winter months for most occupants.

Although this earth-sheltered new house is likely to be the first built for sale in suburban Maryland, similar houses are not uncommon in the Midwest.

Milliner said that high-density Dow Styrofoam was used on the roof and below grade walls and that double vinyl weatherstripping was applied to all of the custom-built windows and doors. He said that moisture protection is provided by a Bentonized trowel-applied system.

Milliner said his firm is losing some money in building this house, which he hopes will bring $144,800. "Costs were indeed greater than expected for a home above ground of similar size, configuration and amenities. However, the energy, environmental and longevity advantages are exensive," he wrote in a report to HUD.

The house will be open for public inspection today from 9 a.m. to 6 p.m. and on Sunday from noon to 6 p.m. A similar schedule will be followed next weekend.

To reach the Terra Vista house, drive north on I-20 and take 70W to 40W and proceed about 9 miles to Harmony Road. Take a right on Harmony and go 1 1/2 miles to Vista Court and left there to the site.