JERRY AND Jan Mumma wanted to have their glass and heat it too. They yearned for an all-glass home, a tree house in the forest. They also wanted to be able to pay the heat bill.

"I've been designing this house in my head for most of my life," said Jerry Mumma, showing visitors around the house in Northern Virginia. He is an architect responsibile for a number of contemporary houses in this area, each one a little more streamlined and modern than the last. He admits his new house owes something to the glass houses of Philip Johnson and Ludwig Mies van der Rohe.

"I've owned the two acres for 15 years. When I finally started the final design, we were in the middle of the first oil crisis. FHA and other government agencies were talking about limiting the glass a house could have to save energy. I decided we could have our glass by designing solar heat collectors as a part of the house."

Mumma integrated the solar collectors into the architecture, unlike the erector set look of too many solar houses.

From the parking space at the road level, you look down on the house. It's shaped like a cross. The arms of the cross cantilever out from the lower, central core. In cantilever construction, the mass is supported only at one point, the rest hangs free. It works the way you balance a tray on one hand.

The first thing you notice are the solar collectors, set above the surrounding flat roof in a cupola. The collectors hang from a steel structuaral system. Skylights roof over the cupola and the collectors.

You walk down a staircase to the house, built on the side of a hill above a stream and an unbuildable flood plain.

On the deep six-sided east porch, as you come in, you can't help but see into the bedroom, the living room and the entry hall.

"It's built for two people and invited guests," Mumma admitted. Virtually every room has at least two walls of glass. Since the glass faces every direction but south, it isn't what you'd call energy efficent. But all the glass is insulated, double glazed.

The house would not work anywhere except in a forest glen, well away from the road and casual traffic. It is a house for adults, a house for people who have no secrets from each other. There are no interior doors, except on the toilet/washbasin compartment and the tub. All the interior walls are closets or storage except for those around the toilet.

Coming in through a 7-feet wide, 8-feet-high sliding door, you are in the entry hall. Most rooms are 9-feet high, a foot above usual. The living room is to the right, the bedroom to the left, the kitchen/dining room straight ahead. The staircase leads below. Above the central core are the solar collectors-they look almost like a hanging sculpture.

The exterior glass is mostly super-size sliding doors. "Eliminating all those mullions and muntins framing the glass, makes you feel as though you're floating in the forest," explained Mumma.

Going into the 15-by-20-feet living room, you see what Mumma means-two walls of the living room are all the glass. Half of each wall slides open to the breezes and the triangular wooden decks. Nothing seems to separate you from the trees, the creek, the woodland green. The fireplace wall has fixed glass on either side.

The living room, like the rest of the house, has minimal furniture: a big soft squishy sofa and two classic chairs, a Charles Eames lounge chair and a Thonet rocker. A handsome antique wooden chest holds a silver pitcher. An oriental rug softens the dark wood floors. "The floors were a real bargain," said Mumma. "They cost $2,000 for the whole house, about the same carpet would have cost."

The kitchen is planned for tidy cooks. The sink and cabinets are on the wall dividing the kitchen from the entry. The refrigerator is set into a continuation of the coat closet (which serves as the living room's south wall).A closed door pantry is on the south. The Jenn-Air stove, which vents through the floor, is set into a double-width kitchen counter.

The dining area is beyond with a sofa for guests. A handsome old drop-leaf table opens for dining. Two walls are glass sliding doors (with screens). Mumma's handsome paintings on canvas are brilliant splashes on the few solid white walls.

The bedroom is on the opposite side of the cross from the living room. The bed may have the only headboard in existence that is actually composed of a walled-in bathtub-actually one wall of the tub cabinet. Doors on either side of the tub open so the bather can enjoy the view. "I thought I'd hate it," said Jan Mumma. "I kept saying, what about the postman?" It turned out that the postman doesn't come down to the house, he leaves the mail in the box at the parking level. And if I really want to, I can close the Venetian blind on the bedroom glass wall. On the other side, it's all our woods."

A bank of closets is set on either side of the tub. This south wall has no windows because it most closely borders a neighbor. A chest of drawers is set into the other side of the bedroom, backing up to the pantry. The toilet/washbasin is almost a cabinet like the tub, with doors on two sides so it can open from the entry hall or the bedroom.

The bedroom shares diagonal decks with the dining room and the entry way.

Downstairs, a bedroom and a bath, with a handsome antique painting from Jan Mumma's family, serves as a guest bedroom for Mumma's three children by his first marriage. A studio for Mumma and the utility room are also set into the central core.

The house's structure and heating system are innovative, to put it mildly.

The solar collectors are set diagonally under the 16-by-20 feet sky-lighted cupola raised above the center of the house's top floor. The surface of the collectors measure 300 square feet, somewhat under the recommended amount for the 1,800 square feet of the house.

"But there's a limit to how many collectors you can put on a house without overpowering it," Mumma said. "And there's also the line you have to draw on the cost."

Because the collectors are hung in a 30-degree angle (the one recommended for this latitude) they also provide a certain amount of shading from the sun for the room below. The collectors are hung from a central structure called Uni-strut, a type of diagonal steel prefabricated system, most often used in industrial construction.

The panels are made of double walled glass mirrored tubes over copper tubes carrying recirculating water. The tubes act as both collectors and radiators of heat, because, unlike most, they have no insulated backing. Mumma had the collectors assembled to his order by KTA company of Rockville. The 20 units cost $250 each.Each is 3 1/2-by-5 feet. The piping for the recirculating water was another $4,500. Hot water is stored in the 3,000 gallon tank ($1,200), insulated with $700 of material. The pumps cost $800. In all, the solar system cost amounted to about $10,000. The tax credit was $2,500. The house also has two heat pumps as a back-up system.

"We've found the sun heats us free for four months of the year-April, May, October and November," Mumma said. "As long as the temperature stays above 32 degrees, we have enough solar heat so the heat pumps don't even kick on."

Despite the glass, the 1,800 square-feet house was heated and cooled for $900 last year. The Mummas only turned on the air conditioning twice last year because of the heavy deciduous tree cover, and the ability of the house to open up 50 percent. The central staircase to the basement serves as a cooling chimney effect. A fan recirculates air in the winter and exhausts hot air in the summer.

Mumma is still working on the solar heat. He isn't happy yet with either it or the house's energy efficiency. He thinks the water storage tank is too large for his collectors, so he may fill it partly with rocks. He's also musing about some way to cover the glass walls on cold winter nights. Both Jerry and Jan Mumma hate curtains and love their outdoor lighting that makes a mysterious forest stage set of their nighttime view. But to save BTU's he's considering using sliding screens.

He'd also like to find a way to make the sun shine more in the winter-he was bitter about last winter's string of dank cloudy days. Another problem he hasn't worked out-how to get the snow off the skylights over the collectors. Most years it would be no problem, but last year it was. It's especially frustrating because if there had been no snow on the collectors they would have functioned extra well, thanks to the reflected sun fuom the surrounding snow. He's working on that problem.

Like most architects, he views his own house as a continuing live-in experiment.

The house's structural system is itself as remarkable as its heating. The upper floor is suspended by steel rods from a Coreten steel girdle that goes around the perimeter of the house. At the center, the house is balanced on four columns-actually 16 huge hollow sewer tiles,set atop each other and filled with concrete.

"They were the real bargain," said Mumma. "They were seconds because they ere pockmarked. I paid $600 for 16. Sewer tiles are made of the best kind of concrete. I'd planned to plaster them, but we've grown to like the way they look."

The rough natural texture of the sewer tiles is pleasant to look at-if you like honest unpretentious materials. The coreten steel frame is also left in its natural, unpainted state. Coreten steel, often used by sculptors, forms its own protective covering by rusting only to a certain point.

The house, not counting Mumma's 10 percent or so architectual fee (which he graciously donated to himself) cost about $125,000 exclusive of the lot. Mumma said it took a great deal of pricing lumber around town to bring it in at that price. The custom-made, double glazed glass doors are Arcadia, sold through Cassidy Co. here.

Mumma did some of the work, principally on the collectors, himself. Hubert Garman of Adelphi, Md., an old friend and a builder Mumma has known for 25 years, was the contractor. "Both he and I were here every day," Mumma said. "If he wasn't here, I called and made him come."

Mumma worked out the structure with the help of engineer Zeron Cohen of Tadger, Cohen Associates. "Jerry won't tell you this," said Jan Mumma. "But the first big party I gave, he wouldn't let me set up tables on the extremes of the cantilevers. But Zeron came over and promised that each extreme could hold as many people as could stand there-more than 100." Mumma added, "the load is worked out to support three feet of snow on the roof and 100 pounds per square feet on the floor at the worst."

The mummas love the house. Even so, they wish they'd had more money to make it larger. They miss living in Georgetown. He has his office there, but is thinking of moving it out to the house. Jan Mumma is duty editor at the Voice of America. she figures the commuting is about 45 minutes one way. She recently was in an automobile accident in which her nose was broken, so she's understnadably unenthusiastic about driving.

"Building a house is a severe test on a marriage," said Mumma. "You can't hide behind anything. You see honestly what each one thinks is necessary and how much each is willing to give-in money and everything else."

For us, it worked out well, because we agreed that the house was important," Jan Mumma said. CAPTION: Picture 1, Jerry Mumma standing under the solar roof; Picture 2, The Mummas' cantilevered glass house; Picture 3, the bedroom with a bath closet behind the wall. Photographs by James A. Parcell-The Washington Post.; Picture 4, Jan Mumma in the Kitchen. By James A. Parcell-The Washington Post