The great brick manson of the old Glover estate on New Mexico Avenue stands empty now amid the untended, seedy splendor of its vast, rolling grounds - awaiting demolition. It is a dying monument to Washington's past and a way of life that is gradually giving way to the high density development of town houses, apartment buildings and offices in an area of the city that was once the special preserve of the very wealthy.

"Really somethin', isn't it?" mused Danny Pumphrey, looking at the mansion as he stood by his truck on the back lawn. He had been drilling in the lush, overgrown garden, testing the soil for the developer who will put up new buildings there. "Be all gone," mused Pumphrey. "Be no more."

In the distance rose the beige, sandstone-like balconies of the Foxhall East condominiums at 4200 Massachusetts Ave. a vision of the future shimmering in the warm autumnal haze.

With the gentle chirping of birds and buzz of insects you could hear the faint growls of earth-moving machines working a tract of land to the north near American University.

Three major developers have acquired ownership or rights to the last remaining undeveloped tracts of land in this area lying south of Ward Circle and bounded by Massachusetts Avenue, Glover-Archbold Park, and Cathedral, New Mexico and Nebraska Avenues.

The 15-acre estate of the late Charles C. Glover Jr., Washington banker and lawyer, is the most recent of these acquisitions. Lawrence N. Brandt, who built the Colonnade on Nex Mexico Avenue and the Beekman Place condominiums on 16th Street NW across from Meridian Hill Park, acquired the tract for $5.6 million earlier this month.

Calling it "the finest piece of property in Washington," Brandt said he plans to build there on the site of the old mansion with its servants' houses and ivy-covered antique barn a "small office building," a 200-unit apartment building and 200 town houses selling for less than $100,000 each.

Brandt said he plans to start construction of the office building within six months and of the other buildings as soon as he receives approval from city agencies.

Just to the north of this old Glover tract lies a nine-acre parcel, so far untouched, where developers Gerald M. LaVay and Richmond Donohoe have plans to put a 525-unit apartment building with units renting for between $337 and $746.

And to the north of this, adjacent to the 5-acre university parking lot, Kettler Brothers Inc., the giant development company that built Montgomery Village, has already cleared more than eight acres where 149 town houses will be constructed. Houses in this development, Westover Place, will sell from about $135,000.

There is big money involved in these developments. Brandt plans to spend more than $35 million, LaVay and Donohoe $20 million, and Kettler $14 million, according to the developers themselves or their spokesmen.

These developments are expected to alter the character of the area by increasing the density of living and business activity along main thoroughfares that are already busy. Residents in both Foxhall East and in the single-family houses of Wesley Heights have expressed concern and some outright opposition. Court and zoning struggles are under way. Yet significant change seems inevitable.

These developments are in the works at a time when city planning officials report a new trend of increased interest during the past two years in residential development in several parts of the city.Town houses are springing up in the far Southeast. Adams-Morgan and Mount Pleasant are seeing a surge of new construction and refurbishment. Plans are afoot to spruce up the city's "west end" just east of Georgetown.

In the Northwest, which contains the city's poshest areas, the change may not be quite so dramatic but city officials say it will certainly be significant in increasing density and pushing up housing values and taxes. The Northwest's empty spaces are filling up.

Perhaps the most publicized example of this was the recent tentative sale for the 25-acre Rockefeller estate on Foxhall Road to a developer who plans to build 100 luxury houses there - a little more than half a mile southwest of the Glover tract.

There seem to be no zoning problems in the way of such a development, and while there are some continuing disputes over the exact shape of development in the Glover area, it's clear to everyone that intensive development of some sort will take place.

Polly Shackleton, the City Council member who represents the area and much of Northwest, bemoans what she calls a lack of comprehensive city planning in the area.

"Here you have these fine established residential neighborhoods, which will be impacted with increased density and traffic and all kinds of things that really could be very damaging," she said. "I think in a way it's too bad we don't have a comprehensive plan."

She said that development of the Rockefeller estate, for example, "will be devastating because Foxhall Road is already crowded. With 100 new houses there, I don't know how we'll deal with it."

Raymond F. E. Pushkar, first vice president of the Spring Valley-Wesley Heights Citizens Association, said that people who moved to the area years ago to live in quiet neighborhoods now find they are inundated by heavy traffic and pollution.

"In the name of tax revenues (the city is) allowing all sorts of development in established neighborhoods," said Pushkar. "As a result we're suffering here from what I might term commercial and high-rise fallout."

Residents of Foxhall East tend to be quite specific in their objections.

Northcutt Ely, an attorney who lives there, said the proposed LaVay-Donohoe apartment building "would tower over us and cut off our sunlight."

Other Foxhall East residents claimed that the Kettler land clearing had caused storm sewer problems for them and that, as a result, water sometimes spurts from their drains.

Area residents said they are concernced that students from the nearby university will team up in the apartment buildings - creating what one person called "rabbit warrens." There is also concern that parking space will be insufficient, or that residents of new developments will park in the streets rather than pay to park in areas provided by the developers.

In each instance, the developers or their spokesmen deny that they are at fault or that they will allow undesirable situations to arise. And they go further.

"I hope not to have any trouble," said Brandt. He said he is proud of what he accomplished at Beekman Place and intends "to do an even better job" at Glover.

Kettler officials pointed out that at least one community group approved of their development, which is lower in density than zoning regulations would allow.

And Whayne Quin, an attorney for LaVay and Donohoe, while noting that their plans are temporarily stalled by opponents, said that the pair is taking a conciliatory approach.

Dr. William A. Holmes of the nearby National United Methodist Church said he had "mixed feelings" about development in the area. "Ideally I'd like to see human beings have as much room as possible," he said.

But, he went on: "That ideal is compromised for me by the reality of the times in which we live . . . It appears that we're moving toward a time when a smaller percentage of people are going to be able to afford single-dwelling houses, and their lack of efficiency in terms of . . . energy and building materials means we have to give serious consideration to the alternative."