THE HENRY and Marjorie Zapruder house was built on a quiet Chevy Chase lane just after the turn of the century. But when the Zapruders decided to add some modern space last fall, they built additions that look as though they'd always been there. And their architect and master builder worked together the way Thomas Jefferson worked with his building crew.

"We'd never worked like that before. It was a new way of building for us," said George Hartman of Hartman and Cox, architects. Hartman designed the addition, three small units connecting the house, and the existing garage, remodeled into a family room. Jim Stokie was project architect.

"We didn't have a contractor," Hartman said. "It would never have worked except Ed Lonergan, a wonderful carpenter, took the job on an hourly basis. He's a master craftsman. He knows so much about building.

"Though we did detailed drawings, every so often he would call us and suggest a better way. Many times he improved our design. On the other hand, since we didn't have a contract, we could make changes as we went along. It was great to be able to say, "Ed, how long would it take to do this or that.' And he'd say, 'About two days.' You can't always get that sort of information from a contractor. Primarily because they don't know because they're not the man doing it.

"Ed did the purchasing, billed to the owner. They paid it immediately to get the discount. And then every two weeks he'd bill them for his hours. The owners saved 25 to 30 percent by working this way. And when an addition can cost $100 a square foot, you can see this was a sizable saving.

"It's the best finished job we've ever worked on. For instance, when the lumber wasn't right, he'd send it back. He could have done the whole thing, but because the Zapruders were anxious to finish before their son Matthew's bar mitzvah in December, we got in William Merce of Kensington, another fine craftsman, to do the framing."

The addition, in deference to the client's taste and Hartman's convictions, follows closely the style of the original house. This is a departure from the way modern architects used to philosophize about houses, when additions had to tell their time.

Hartman has designed many additions and remodelings in Chevy Chase. He has an understanding of what makes those houses work, and not work.

"Several houses in the neighborhood have additions that show their years," Hartman said. "And I think they look cluttered. The Zapruders' main house is very neat. I wanted to do an addition that would blend with the house and as [Washington architect] Hugh Newell Jacobsen says, be polite to the neighborhood." For this reason, even the windows of the addition are mullioned like the windows of the house.

"We tried it both ways, we had Ed hold up frames with and without," Hartman said. "But we liked it better matching. The new addition connects the house and the garage; both had small paned glass, so it seemed appropriate to match them. We were much more conscious of keeping the same style outside. Inside, the rooms are all designed to serve today's way of living."

Hartman's addition is in four units, as though each had been added as the need came, marching down the back yard to meet the garage. The effect is almost telescopic, as though the two middle ones would slide into the bigger one. A similar ploy is currently a favorite of architect Hugh Newell Jacobsen. Twenty five years ago, in the Robert Lee house in Georgetown, Jacobsen added a wing that's almost a carbon copy. In one of his recent houses, the units all face the street. Each unit of Jacobsen's (like one of those wooden Russian dolls that all fit inside each other) gets smaller and smaller until you end with a dog house. Hartman hasn't gone that far here.

The Zapruders realized when they bought the house in 1975 that as the children grew bigger, the house would have to as well. Though these houses are grandiose on the outside, the rooms are not as large as you might think. And the floor plans are dedicated to a way of living much more restrained than now. Back then, anyone in the double parlors had to have on their best suits and behavior.

Anyway, back then, entertainment was not as noisy as it is now. Phonographs, if you had them, and radio, when it came, were far too expensive and awesome to be something continually used. They were reserved for state occasions and kept closely under parental control.

The Zapruders are great movie and music fans. So it was soon obvious that there needed to be an informal living room. "We talked about it for five years, three of those with George Hartman. We finally decided that the children would be grown and gone if we didn't go ahead with it," Marjorie Zapruder said.

The first unit is a morning room or sun roon, built where the back porch once stood. The room has a peaked ceiling, going up to a dormer that serves as a skylight. A window seat -- "I told George I wanted a window seat most" -- sits under a sunny window. Shelves on either side display books and treasures. A big oak table sits in the middle of the room and serves for homework and informal suppers. Its five antique chairs, found recently, just match two the Zapruders had been given by Marjorie Zapruder's mother. Hanging over the table is a magnificent Austrian mid-19th-century chandelier said to be from a palace, the gift of Henry Zapruder's mother.

French doors from the new sun room lead onto an east dining deck, with its own pergola, built under the great Palladian window of the original house. By rights, there should have been an equally grandoise French door under the window, but the stair comes up there.

A hall runs parallel to the room, with pantry closets built in on either side of a niche with a dormer above.

The second unit is the family entryway and mud room. Twin sets of French doors, with twin dormers above them face each other across the hall. One set of doors opens onto the dining deck, the other to a landing porch off the driveway. A huge tree carefully surrounded by the deck, kept the driveway from going into the garage at the rear of the lot. Four big closets, one each for the children and one to hold spare coats and gear.

The third unit continues the hall, with a bathroom, complete with shower, and a laundry closet. The hall is floored with brick. The hall ceiling, like the small dining room, goes up in the same shape as the peaked roof. The ceilings are floored and painted white, much like the horizontal paneling often used on back porches. A round porthole window lightens this area.

The fourth unit is the house's original garage. A movie projector is built in, along with closets for stereo equipment, the addition's gas and air conditioning equipment, and shelves for collections. A comfortable sofa, and two Wassily chairs serve the adults. A ping-pong table is for the kids. Track lighting is built into the beams, but a multiple armed lamp makes it possible to read or play the game of Go. "We think the equipment is beautiful," said Marjorie Zapruder, "but we haven't been able to translate the directions from the Japanese."

The views are all of the garden presided over by George Higashi.

The old part of the house is a fine setting for Marjorie Zapruder's art historian tastes. (She takes on free-lance art projects now. Earlier she was registrar with the National Collection of Fine Arts. She also worked at the White House in the women's affairs office during the Carter administration.)

Her tax-lawyer (with Cohen and Uretz) husband and their three children (Matthew, 13, and the twins, Michael and Alexandria, 11) share her taste. Half of the objects look as if they came from the Museum of Modern Art's Design Collection.

The double living room is full of French turn-of-the-century posters. A big ICF sofa has been ordered for the front room by interior designer Ann Hartman. The room already has an elaborate stereo storage by Smith, Thomas and Smith, cabinetmakers, and an amazing game table that folds out to provide space for backgammon, chess and some things nobody knows how to play.

Corner fireplaces separate the two rooms.

The back parlor has a Mies van der Rohe coffee table complete with an orchid as well as Alvar Aalto stools.

The dining room has a wonderful bicycle-wheel serving cart and a Daum glass vase. The table, except when it's in use, is covered with a grand 1930's quilt, with all the Art Deco colors: peach, pale green, and yellow to match the walls. A country French blanket chest serves as a buffet. A Victorian mirror came from a house-hunting expedition.

When Marjorie Zapruder frist saw the house, a handsome 1900s clapboard colonial, she knew husband Henry would flip over it, as she had. Best of all, from their standpoint, the house was owned by an old couple in their 90s who'd never driven it off the city streets.

"It was wonderful because it had not been touched since it was built," said Marjorie Zapruder. "No avocado kitchen to offend the eye. It even had the original stove."

Before they moved in, the Zapruders had the hard things done, new wiring and plumbing, and, because the Zapruders are great cooks, an expansive kitchen for entertaining. A friend, who was an architect, Ted Oldham, now of Skidmore, Owens and Merrill, designed it for them.

The kitchen has all white cabinets with a big island in the middle for chopping (both with knives and teeth), and buffet service. A new pot rack hangs above the island, made for the Zapruders by Michael Semsch of Fairfax. The old pantry came out and two new sinks, one double, the other bar, were installed in the new counter. The ovens are built in as is the refrigerator.

The kitchen has the Scandinavian bean-and-spice rack that everybody into Modern had to have in the '60s. All of these good designs are mixed in with antique pieces, some from family, some found in out of way places.

It all works together to make a setting that suits the Zapruders, Hartman, Lonergan and the neighbors. Not many houses can make that claim.