If you're poor and black and live in one of Washington's public housing projects, you live in a city unknown to many Washingtonians and most visitors to the nation's capital. You live in a city within a city, so isolated that you may believe that someone in the other Washington has intentionally set you apart from the rest.

"It's not just a coincidence that the National Guard is on one side of Anacostia and Boiling Field is on the other," said Stanley Anderson, a former city councilman from Anacostia. "It's meant as a form of control in the event of trouble."

Just about everyone you know is, like you, poor and black. "I want to meet me a nice, white friend," said Donna Williams, "because they've had more experience. They've had better things."

To travel into The Projects from the Washington of palatial government buildings and tinted glass office towers is to travel not just into another city, but another world. The landscape, the faces, even the language are different, almost foreign, to the visitor, particularly the white visitor.

There is no need to travel even as far as the other side of the river, into Anacostia, to find this other world. It exists throughout the four quadrants of the capital, wherever poor blacks live in tight concentrations, in projects, fenced off from the Washington of big government and big business.

The isolation of poor blacks here grows tighter daily as more whites return to the city, buying and renovating houses on streets where they would not have walked in broad daylight even a year ago.

For the citizens of Washington as a whole, the replacement of decrepit row houses by expensively renovated town houses is a two-edged sword. The whites who now feel more comfortable strolling through these formerly blighted neighborhoods see the change as an improvement. Now, they and their children may enjoy the benefits of in-town living.

Many learned to their chagrin that they and their children, surrounded in the suburbs by people who bore no recognizable difference from themselves, had grown listless and troubled. In a very real way, they fould themselves in a predicament ironically like the one facing many poor blacks in The Projects: life in an artificial atmosphere is empty.

But from the poor, black viewpoint, the appearance of quaintly decorated town houses on what had been their turf is ominous. It is an encroachment by affluent whites on black territory and it is heightening tensions in their isolated world.

Diane Moore pointed out the window of her apartment in Potomac Gardens in Northeast Washington at a row of former slum dwellings undergoing renovation. "Those houses will sell to whites for $70,000 to $80,000," she predicted, "and that white man ain't going to take kindly to snotty nosed nigger kids running around his front garden. I'm sure we won't be here much more than another year or two."

Moore's friend, Linda Keyes, a day care center teacher, disagreed: "Oh, no, Diane. This is government housing and no one's going to push us out of here."

But Mayor Walter Washington's inner city trouble-shooter, Sam Jordan, lent some credence to Moore's fears. He pointed out Green Leaf Gardens in Southwest Washington, one of the older and shabbier of the National Capitol Housing Projects, which is completely ringed by expensive highrise apartment buildings and townhouses, several of then the residences of senators and congressmen.

"They've been trying for years to squeeze this place out," Jordan said. "And I don't doubt that they'll succeed. I wouldn't give this place more than two or three years."

The history of public housing in the District of Columbia goes back to 1934, when an Alley Dwelling Authority was formed to reclaim back alleys and other slum areas. These were the classic black slums of a sleepy Southern town, with tumbledown sheds and outdoor privies.

Project-building peaked in the years around World War II. The developments were intended to provide temporary housing, first for the influx of war-related workers into the capital and, afterward, for the city's poor. But what was supposed to be a stopgap measure has become a permanent feature of Washington and scores of other U.S. cities.

The Projects of 1978 - even at their worst, with boarded-up windows, abandoned cars outside, obscenities spray-painted on the walls, garbage strewn on the bare courtyards - bear little resemblance to what the Alley Dwelling Authority reconstracted.

In other cities, other countries, The Projects of Washington would be considered pretty good housing. In New Delhi, for example, middle-ranking civil servants live in government quarters not markedly different.

But, for The Project people, life in the developments carries one distinct similarity to the World War II days when the Projects were legislatively designated for Negroes and whites): poor blacks are isolated from the white mainstream of Washington.

Some experts believe that isolation is a major contribution to a vicious cycle of crime and victimization in The Projects: fearful that they might be assaulted, a large number of Project residents depend on taxis rather than waiting on lonely streets for buses. Taxi drivers, also fearful of being attacked, try to avoid fares to and from The Projects. Thus, isolation is heightened and crime spreads.

Noting that only 11 percent of residents at Arthur Capper Dwellings, just a 10-minute walk from the Capitol in Southeast Washington, owned cars, a recent survey prepared for the U.S. Department of Housing and Urban Development found that "the crime problem has contributed to the isolation of Capper Dwellings residents."

It's not at all unusual to find young people in The Projects who have never met a white. Certainly, most have no white friends or even casual acquaintances.

Donna Williams, who is 16 and in the 10th grade at Randall High School in Southwest Washington, said she believed that whites were "proper." This, she said, meant that they "know how to do proper things like what to order in a restaurant, how to set a table nice and how to talk proper."

In areas like Green Leaf Gardens and Potomac Gardens, where the worlds of The Project people and the affluent whites abut each other, there is frequent tension and occasional outbursts of violence.

"Oh, I don't mean they're always at each other's throats," Sam Jordan explained. "But there's harassment, muggings from time to time, purses and credit cards snatched."

Thus, not surprisingly, the dividing line is money. "Washington is a black town and we have a black government," said Michael Harrison at the Kenilworth Courts project, "but money is white. And that's what we don't have."

On the other side of the line, in a rambling, tree-shaded Cleveland Park house near Washington Cathedral, a white lawyer with the Department of Agriculture put it this way: "I've lived in Washington for four years and I know, because I read it somewhere, that the population is 72 percent black. But I can't believe it. I just don't see that many blacks around. Not poor ones, anyway."

The lawyer doesn't have to see them, because he does not go looking for them. To travel into the world of Washington's poor blacks is seen as looking for trouble - harassment, muggings or worse. And the poor blacks have no need and little opportunity to travel into the other world of Washington.

Harrison, who has the opportunity - unusual for a project dweller - to travel back and forth across the line, said ignorance is a key factor. A political science graduate of Federal City College, he works as a tour guide for Landmark Services Inc.

"Whenever I take a group of tourists around," Harrison said, "they'll usually comment about how beautiful Washington is. Of course, that's true. But I often try to tell them about the other Washington, away from the monuments, so they can get a more accurate understanding of the capital."

Harrison said he was "amazed" about how little the average American tourist seemed to know about Washington, "how little they understand the problems of most of the people who live here."

As an early spring rain pounded the muddy courtyard outside Kimi Gray's apartment one recent morning, she and Harrison and another Kenilworth Courts resident, Betty Cohens, came to the conclusion that many whites came to the capital for relatively short periods, to work for one government agency or another. "People like that aren't really interested in this city, as such, said Harrison. "And what do blacks folks have in common with them." Gray asked, "with their great big horses and their fancy little sports cars?"

"If a young, white girl gets pregnant," Betty Cohens said at Kenilworth Courts, "her parents can send her off to her aunt in England to have the baby and no one will know about it."

Then there's the belief among some blacks who once had regular contact with whites that they lost interest in black problems when the focus changed from civil rights to economic issues.

"I guess you could say that poverty, black poverty, isn't a hot issue, the way the rights movement was," observed Anderson, the former city councilman. "I hardly ever get to see my old friends in Cleveland Park any more."

Anderson, who owns an old house in Anacostia, pointed out to a visitor that the isolation of the area was not simply a matter of it being separate from the rest of the city by the river. "It's intentional," he claimed.

It's common to hear in Kenilworth Courts, as well as in other Projects, that isolation is increased by inadequate bus routes, an almost total absence of taxis, and an approach road system that puts the developments in the center of virtual maze of streets.

"One thing I'll give you white folks credit for," said Kimi Gray. "You certainly know how to divide us. You do that real well."

While it is convenient to point the finger of blame entirely at whites, a number of introspective blacks, in The Projects and outside them, say that black apathy is a core reason for continuing poverty and the isolation of the poor.

"It's a fact that poor blacks don't vote," said City Councilman Douglas Moore. "So, in turn, politicans don't respond to their needs." Moore, who has fashioned a role for himself as a maverick on the council, claimed that he, alone, genuinely represented the poor of Washington. "I do it because I have a passion for poor people."

Miachael Harrison, however, sees little difference between Moore and the rest of the council members. "They're all out to care for themselves. They take the poor people of this city completely for granted."

What, if anything, did he think could be done to change this? "The poor people of Washington must be taught that the vote is the most powerful, the only, lever we control," Harrison answered. "We're going to have to find our own leaders and then use our votes to put them in power. There's no other way out for us."