IN LATE SPRING and summer, Norman and Charlanne Harrington sometimes sit smugly in their kitchen. Screened by their front porch ship's carpenter gothic woodwork, they watch the show, the passing parade of tourists. Sometimes 8000 a weekend come by bus, boat and car to the tiny town (800 pop.) of Oxford, Maryland.

The tourists stare back, admiring the Harringtons' white cottage and cherry trees. Ah, nostalgia.But if you look a bit closer, and don't have your eyes all fogged up by the quaintness of it all, you'll see that to the side of the original 1880s house is a splendid contemporary addition. The design is by William P. Lecky of the Kent Cooper Partnership, a Washington architectural firm.

The new wing doesn't shout its presence. You have to walk thirty feet back from the sidewalk, through an entry court paved with bluestone and screened this time of year by a mass of cherry blossoms. The Harringtons laugh and admit that, like all the cliches about modern architecture, it isn't easy to find the front door. First-time visitors sometimes turn up at the "back" or kitchen door on the front porch. But such is life.

Anyway, once you have followed the bluestones (intended to set your feet in the path of righteousness), you come to a bright Chinese red door with slits of glass on either side and topped by a great triangle of glass. The new addition, for all its glass and red, is that most traditional of afterthoughts, a lean-to shed, covered in the ubiquitous Oxofrd-white siding.

The house thus pays its respects to Morris Street's antiquities - across the street is Academy House, circa 1770, the second oldest house in town. It isn't far to the Robert Morris Inn and the waterfront.

But once inside the Harrington house, the years drop away in a hurry. The front hall, paved again with the bluestone, is lit with a wonderful skylight, paced with baffles to shield the interior from too much summer sun. You then go through a generous doorway into the twenty-four-by-twenty-four-foot living room, stepping down as you go, the better to admire the steeply sloping ceiling. The ceiling, in a manner of speaking, is floored. It is covered with a dark-stained oak flooring curling down at the wall to make cove lighting. A great burst of color over the sofa is not a painting but a handsome piece of Scandinavian fabric by Peter Condu that the Harringtons bought in Stockholm. A slight ledge at the back of the room sits under the glass wall and leads you out to the floating deck. From the vegetable patch at the back of the deep (180 feet or so) lot the addition looks every so slightly like a ship's mast.

The living room on one wall soars up to meet the balcony den, an expansive fourteen-by-twenty-foot room with a bookshelf railing.

On the street side is the aforementioned kitchen, the original living room of the house, opening onto the porch. On the other side of the dining room is the master bedroom, at the back of the house.

Upstairs, in the old part of the house, over the kitchen, dining room and bedroom, are two more bedrooms and a bath, and a darkroom for Harrington, a serious photographer. The large den upstairs has one wall of the original house removed to provide an overlook into the living room.

One of the Harrington's three sons, Scott (they have two daughters as well), who has worked as a draftsman and model-maker in the architectural office of Kent Cooper, helped on the entire project.

Lecky, the firm's partner-in-charge, decided that "with the exception of the floors, the interior had to be gutted. The existing house was not only too small to meet their needs, it had no plumbing, heating or electricity to speak of, and was badly in need of repair. Yet the lot was large enough to take an addition, it was a lovely street, and the house had historic significance. The exterior architectural problem then became not only one of adding a contemporary addition to a historic building, but also making an overall design that would be harmonious with the Oxford streetscape."

Construction was quite a job. One whole side of the house had to be removed to unite the two structures.

The project was not cheap. The old house and lot cost $34,000. Harrington figures that with the remodeling, landscaping and such, they probably have close to $155,000 in the property.

In any case, on these spring days, when the tourists start to pile into Oxford, the Harringtons feel very good about being inside looking out.