ABOUT THREE years ago, Harry Montague--architect for the remodeling of half of Cleveland Park--was asked by a real estate agent to look at a house, "and tell us what, if anything can be done to sell it."

The house was, to put it mildly, not in first-class condition. The roof leaked. The plaster walls and ceilings had not been improved by the roof leaks. The front porch roof was beyond repair. The kitchen had not been brought into the '80s. Appalled by all of this, the real estate agent priced the house at $89,000, perhaps the lowest price for a Cleveland Park house in the past five years.

When Montague heard the price, he didn't ask twice. On the spot, he said, "I'll take it."

Believe it or not, the remodeling and rehabilitation cost was under what he paid for the house, a remarkably small amount in this day and time for that much work. But then, Montague not only did the design and some of the general contracting, but much of the framing and miscellaneous carpentry, dry wall work and painting. His wife, Ruth Montague, an architect with the World Bank, helped with all of it. Daughter Ellen, 21, and son David, 19, both of whom have worked on construction jobs, also pitched in. Even so, the last work is just being finished in time for the Cleveland Park House Tour next week.

The Montague house is one of eight Cleveland Park houses open Sunday (April 25) from 1 to 5 p.m. to benefit the National Child Research Center. (Call 363-8777 for ticket information.)

The leaking roof, the house's worst problem, was not such a deterrent to Montague. He put holes in it anyway, 13 of them to be exact--13 skylights. He also added a pitched roof for the porch, which he thinks is more in keeping with the style of the house. Another addition: a cupola, just a bit off center, with a lantern (those are the windows at the top of a cupola).

On the outside, the house already had pediments over the dormers and second-floor front balcony, both ornamented with an Art Nouveau scroll.

Montague copied the pediments for his new front porch roof and the lantern. "When I went for the permit, the building inspector said, 'Oh, you've put a pyramid atop your house. That's very lucky, very healthy.' And he pulled out a book from under his counter about pyramid power."

The front porch, by the way, is unusual in that it has steps on either side.

The Montagues liked many things about the house besides the price. "The back of the house faces south," he said. "We get sun in the family room all day long. We don't need furnace heat at all until night."

They also liked the wonderful leaded-glass windows. An oval window set with leaded glass lights an alcove just right for the piano.

Montague didn't have to bring in columns as the Post Modern architects do. The living room, in high 1908 style, already had columns defining the piano alcove and marking the separation between the double living room. Montague used Woodmode prefabricated bookcases on all available walls of the back half of the living room, turning it into a comfortable library.

He also reworked the stair so it would go up straight, instead of turning. This allows the front hall to go all the way through from front door to the deck door and gives an entrance to the kitchen from the hall. Before, you had to come into the kitchen through the dining room.

The biggest additions to the house are the 14-by-14-foot family and informal dining room and the adjoining back deck. The family room extends the old kitchen, and its ceiling goes up to a steep triangle. Six of the house's skylights are in the new room. Glass windows go around two sides of the room. All the skylights and the new Pella windows, with roll-up screens, are double glazed.

The room has some handsome pieces of furniture. The refractory table is 250 years old and was handed down by Montague's father. Baskets are used as drawers on the refractory table's shelf. A round table, chairs and a wonderful Morris chair came "like everything else in the house, my wife says, from garage sales," according to Montague.

A balcony over the kitchen section was originally a rather useless upstairs space. The Montagues put a one-piece compact kitchen there while the main kitchen was under construction.

The remodeled kitchen kept its original tin ceiling, and gained wall-to-wall Woodmode cabinets and shelves. "I used top cabinets as lower cabinets," said Montague, "because they are shallower. Then I used open bookcases for the top units." The stove and refrigerator are set into the cabinets.

Cans, glass and china, herbs and pots and pans are all arranged on the shelves as decoration. The counter space is concentrated into an island with a Jenn-Air cook-top unit. A handsome greeny-brown American tile from the Tile Gallery covers the counter top. "I'd been using Mexican tile," explained Montague, "but it does chip."

Upstairs, the Montagues tore through a ceiling and a wall to give son David a two-story bedroom and balcony, with, of course, skylights. David finds a wooden construction ladder is a fine way to reach it. The room is decorated with his collection of musical instruments.

Ellen's room has access to the cupola. Though its floor is 3/4-inch acrylic, to light the hall below, Ellen has put her mattress on it and slept there. Her room is also skylit. "They all love sleeping under skylights, and looking up at the moon and stars," Montague said.

When all those who have hired Montague to remodel their houses come on the tour Sunday, they won't be a bit disappointed.