The north side of the 2800 block of P Street NW is a Georgetown rarity. There are just four homes in three pre-Civil War buildings, with nicely landscaped yards and gardens between, huge trees and a stone fence topped by rifle barrels made for the combatants in the War of 1812.

It's a green, almost park-like oasis that some of the block's residents, including Alice Acheson, the 88-year-old widow of Dean Acheson, President Truman's secretary of state, think should be preserved against the encroachment of further development.

But Tom Elmore, the 39-year-old civil engineer who lives in the middle of the block at 2811 P St., has decided to sell the side lot adjacent to his house for more than $300,000 to builder Michael Minkoff so that he can attach a $1.2 million row house.

The construction proposal has now erupted into a public neighborhood dispute over two basic values -- Elmore's acknowledged right to develop his residentially zoned property as he wishes against the aesthetic wishes of his neighbors, who view more development as an intrusion on their own in-town escape from the congestion of much of Georgetown.

"I own the lot," Elmore said yesterday. "I plan to develop it. I have the right to develop it.

"I'm going to do something," he said. "I'm a North Carolina boy. If I can't build on it, I'll see if I can't raise a few hogs or else I'll invite all the derelicts in Georgetown to come over and pitch their tents."

Acheson, who has lived at 2805 P St. for 62 years in a house that is separated from Elmore's by his side lot and Acheson's walled-in garden, complained that she learned of the proposal only a week ago.

"He didn't tell me what he was proposing," she said. "I'm surprised and utterly annoyed. It's practically the only block that has this much open space. They're killing Georgetown by overbuilding.

"My trees would have to come down," she said of the giant magnolia and flowering cherry that are rooted in her garden, but hang over the air space of Elmore's lot. "I don't have too much sun now and then I'd have a brick wall next to me."

Elmore said Acheson's trees would have to be pruned, not cut down. "I enjoy them, too," he said.

Acheson and two other neighbors, Don V. Harris Jr., a partner in the Covington & Burling law firm, where the former secretary of state once worked, and educational consultant Anne Childs, trooped to the Commission of Fine Arts earlier this week to protest Elmore's plans in vocal terms.

"I'm opposed to any house on that lot," Harris said. "This is one of the few blocks that has not been junked up."

The commission, which acts as an advisory arbiter on the architectural beauty of development proposals in much of Washington, unanimously recommended against construction of the row house. The Georgetown architectural review board, an advisory panel to the Fine Arts panel, had already said it favored the project.

"I'm chagrined that there's an attack on this marvelous block," said one commission member, Chicago architect Walter A. Netsch.

The commission's chairman, J. Carter Brown, director of the National Gallery of Art, said, "We have a tradition of not going along with the zoning parameters. My own view is that it should not be built."

Minkoff said the commission's recommendation was merely an effort to "make an accommodation to Mrs. Acheson. The decision by the Fine Arts Commission is advisory and the city can do as it likes."

Minkoff said he intends to try to get the city to issue a building permit for the project. He noted that in a similar case, a block away on Q Street NW, the Fine Arts panel recommended that two lots be left vacant, but the city approved construction on them and was upheld in a subsequent 1977 lawsuit.

Elmore said he needs the money from the sale of the lot so that he can expand his own two-bedroom house, now valued at $346,886 by the D.C. tax assessor.

"He's certainly entitled to build a house there," Childs said, "but it's really a question of preserving the character of the block."

Harris and Acheson have granted open space and facade easements to the Foundation for the Preservation of Historic Georgetown, which, among other things, prevent the alteration of the fronts of their semidetached houses.

Harris has tried unsuccessfully to get Elmore to grant the same easements for his house and lot. "Tommy's okay," Harris said, "but he doesn't have the respect for the old village that we do."

Elmore said he has not granted the easements on his house because the donation "doesn't offer me as much" in tax credits as the sale of the lot would.

"I'm as much a preservationist as they are," he said. "Every single brick on my house has been brought back to its original state."