A generation ago, the children of Foggy Bottom thought of 26th Street as their amusement park.

At the corner of M Street was the long-abandoned Sealtest Dairy. It was a spooky boxcar of a place - perfect for scaring the wits out of a younger brother, or hiding "treasure."

At the corner of K Street was a ball field. Eight months a year, a Sunday softball doubleheader was played there. Twelve months a year, one as good a view of Georgetown, the Potomac River and the Virginia hiils as could be found in Washington.

This summer, the view will be the same the landscape will be very different. By July, Potomac Overlook and Westbridge will have opened. They will be the first substantial projects to be finished in the rapidly developing West End.

Potomac Overlook, a nine-story, 50-unit condominium apartment house, will sit on the infield, at the northeast corner of 26th and K. Its emphasis will be on simplicity and privacy, and its feature attraction will be what the name implies - at least on the third and above.

Westbridge will replace the dairy. Half of it will be a nine-story office building. The rest will be a 10-story condominium apartment house. Westbridge's emphsis will be on luxury and its trademark will be a view of Rock Creek Park and Georgetown.

Only 200 yards apart, the two complexes will form a kind of western front for the West End - an area bounded by Rock Creek park on the west, K Street on the south, New Hampshire Avenue on the east and N Street on the north.

But the other fronts are coming. Oliver T. Carr Co., developer of Westbridge, had broken ground for an office building at New Hampshire Avenue and M Street NW, where the headquarters of Goodwill Industries once was. Along the northern edge of the West End, at least four developers are planning at least six housing projects.

And the middle will soon follow. A Guest House hotel is under construction in the 2500 block of Pennsylvania Avenue NW.

But Westbridge and Potomac Overlook will house the first new crop of permanent residents. Both developments have sparked great interest among prospective occupants.

William T. Brawner, president of Brawner Construction Inc. and developer of Potomac Overlook, said he had received more than 300 inquiries about the 50 units as of this week.

"Most are young married people with two incomes and most live now within five blocks," Brawner said. "They like Foggy Bottom and its proximity to Georgetown."

Brawner said he originally planned 10 townhouses for the Potomac Overlook site. But he changed to a high-rise when he realized that the only view from a townhouse would be of a traffic jams along K Street and the Whitehurst Freeway.

Potomac Overlook will cost $3,465,000 to build. Condominium sales prices will range from $47,000 (one bedroom with an alley view) to $140,000 (pent-house with a river view). Condominium fees are expected to total about $80 a month. The building will have a brown brick exterior.

Westbridge, meanwhile, is only about half up. The office building, on the northeast corner of 26th and Pennsylvania, is nearly finished, and ground has been broken only recently for the apartment building, which will be directly to the east.

When finished, Westbridge will contain 157 apartments and about 60 offices. Parking will be one level below ground, and small retail shops will occupy the ground level across the whole complex. The complex will have burgundy brick facing with the black aluminum trim.

The office building will cost $12.3 million to build. The apartment will cost $13.5 million and are expected to be occupied in June 1979.

Project manager Robert Carr said more than half of the office building's 175,000 square feet had been leased as of this week. Tennants will include "a lot of lawyers, a lot of accountants," Carr said. Apartment nibbles have come so far from "mostly middle-aged professional people working down-town," he said.

The philosophy of teh project is simiral to Watergate in that we're trying to build a project big enough and appealing enough," Carr said. "We thought about townhouses, but it was our opinion that that wasn't economically feasible."

What has been planned instead is a complex of "luxury. Not superluxury, but very good quality," Carr said.

Westbridge office space is expected to go for about $8.50 a square foot. Condominiums are tentatively scaled from $65,000 to $160,000.

Neither developer consulted neighborhood residents about the design or nature of his project, adn neither said he felt it necessary. Both said no complaints have been received.

But the effects of the two projects on Foggy Bottom will be considerable.

The most noticeable effect will be architectural incongruity. Both developments are being built right beside rows of turn-of-the-century townhouses. While the townhouses just east of Westbridge are unoccupied and scheduled for eventual demolition, they will not "blend" with their new, modern neighbor the way most new commercial development has "blended"" with the townhouses of Georgetown.

Another effect will be to make a difficult parking situation even worse. Neither development will provide as many parking spaces as it will have tenants and residents. As a result, competition for parking spaces on local streets is expected to increase.

In addition, some neighborhood merchants, many established in Foggy Bottom for three decades or more, will face threatening competitors in Westbridge. A liquor store and drug store already are planned in the Westbridge office complex. They are expected to go head-to-head with the two liqour stores and one drug store on nearby Pennsylvania Avenue.

So 26th Street, full of dump trucks and cranes these days, is heading into a period of major change. And for the West End as a whole, it's only the beginning.