The invitation reads "from 6:30 till dark." We drive through the Washington streets, into the heart of the Northwest ghetto, past dilapidated houses, boarded up storefronts and apartment buildings with empty windows.

Following written directions, we turn right off 13th Street and, searching for a parking space, cruise slowly past our destination. It is easy to spot: A young white couple is on the front steps, talking.

The street scene is out of a James Baldwin short story or a Lonne Elder play: an odd antiphony of life and decay. Old men in dark, thin clothes sit quietly on stoops, their hands folded between their knees. Shirtless boys race on battered bikes, shouting instructions to one another.

Young men, and some women, in their late teens or 20s crowd around cars, on corners, in front of houses, talking and jiving, sometimes spilling over into the street.

Transistor radios blare; buses and cars rumble and screech; occasionally a dog barks.

Weeds sprout in empty lots and front yards, from under fences, between cracks in the sidewalk. Bottles and cans are everywhere. Worn, abandoned furniture is strewn about.

The buildings are mostly brick and stone, apartment houses interspersed with smaller residences. Some are boarded up, their windows blank, fences broken or falling down.

Even so, many are intriguingly designed, reflecting the attention to detail and workmanship characteristic of an earlier period. Compared to these, the newer projects occupying several nearby blocks are bland and unimaginative.

We enter a three-story red brick building standing between two similar structures, narrow but deep. The large windows are boarded on the first floor but covered by plastic sheathing higher up.

As we walk inside, it becomes immediately clear why the invitation said this would be a "shell party." Walls and ceilings are stripped, the floor is bare. Wiring hangs loose, pipes and ducts are in plain view. Two-by-fours frame out old closets and rooms; doors still hang anachronistically on their jambs.

On the second floor the party is taking place. Drinks and food are spread on card tables and makeshift counters. On one wall hang architect's drawings, together with a sign warning that the design already has been changed. A suggestion board is dotted with notes, some serious, some comic, others obscene.

The guests, who wander throughout the shell, are all white; most are around the age of the hosts, a young "professional" couple.

They are part of the "white return" on which many city planners are pinning their hopes for an urban revival. Like thousands of others around the country, they are coming in from the suburbs, seeking the excitement and conveniences of city life, as well as the housing bargains available in the depleted core.

And a bargain they seem to have found. The building, already stripped by the previous owner, cost them $28,000. In some neighborhoods the value of shells and old house has inflated astronomically, driven up by speculators cashing in on the back-to-the-city movement.

But this area still has good buys, the hostess tell us, "because it's east of 14th Street," the center of the riots that devastated the city in 1968.

To complete their elaborate plans, which will cost $80,000 to 100,000, the couple has applied to the city government for a 3 percent rehabilitation loan. In inflationary times, of course, that is almost free money, a virtual bribe, a downpayment against the increased property taxes the building and its neighbors ultimately will generate.

Our hosts plan to rent out the basement apartment to further lighten their financial burden.

Those tenants will be the building's only other occupants. The couple has no children, nor do the architectural drawings provide for any. At one time, the building was home for many people; the door on what will be the master bedroom still bears the impression of the number six.

The drawings comprehend a lifestyle the former roomers, and the neighborhood's present dwellers, could never hope to know. The master bedroom will feature a vaulted ceiling, a skylight, a fireplace. A bridge, crossing a three-story skylighted stairwell, will enter an equally large combination bath and utility room, complete with sunken shower, which in turn will lead out onto a rooftop deck and garden.

For now, the view is anything but attractive. The backyard is a jumble, a nearby parking lot is strewn with rubble, other houses stand in various stages of deterioration. But soon, certainly within a decade, this neighborhood will be "revitalized," its present residents scattered, few scars remaining from the conflagration that followed Martin Luther King's assassination.

We prepare to go. "We're not responsible once you leave the house," the hostess says, only half joking.

Descending into the gathering dusk of the warm summer evening, we are perplexed once again by the abundant contradictions. Is there no way to rebuild our cities without driving out those who have suffered through their decay? Why can't these residents benefit from the improvements that will accompany the affluent newcomers?

Must we destroy these neighborhoods in order to save them?