Washingtonians may recall the 1978 case of George and Lillian Blackburn, an elderly couple who, over a period of some six months, were beaten by teen-age thugs who robbed them of their Social Security money, broke her leg in two places and, for a brief time, actually slept in their apartment, which they used as a base for their other criminal activities.

"We had no way to force them out," George Blackburn told reporters after he and his wife were rescued by social workers.

It was one of the saddest stories I've heard. I was reminded of it by a more recent development.

A Washington Post story a few days ago told of a pair of Northeast D.C. housing developments whose grounds have become an open-air drug market, controlled by New York dealers who have taken over the apartments of local residents.

According to the story, dealers who want to move in on the Mayfair Mansions-Paradise Manor drug market usually locate a drug user -- "often an unemployed woman receiving welfare whose drug habit exceeds her ability to pay." They then "supply the resident with drugs in exchange for the use of the apartment."

Now there are obvious differences between the physical intimidation of an elderly couple and the methods used by the New Yorkers to take over the lucrative "Mayfair Market." But there are similarities as well.

In both cases, the criminals exploit the weaknesses of their immediate victims and then proceed to victimize an entire community.

It is in some ways an analogy of what is happening in large cities across America. Detroit, which has become the murder capital of America, may be the worst case. Huge swaths of the city have been taken over by heavily armed drug-dealing gangs, chasing Detroit's middle-class residents to the suburbs.

But a similar trend is under way in other cities: East St. Louis, Milwaukee, Los Angeles and Washington.

Occasionally, residents fight back, with varying degrees of success. In Washington, for instance, residents of some neighborhoods have enlisted the aid of the police in at least forcing the open-air drug dealers to relocate. Here and there, streets have been closed to nonresident auto traffic in an effort to deprive the dealers of their customers.

But nothing seems to work very well. The well-off residents of one regentrified Washington neighborhood -- Logan Circle, a longtime hotbed of street prostitution -- not only enlisted the assistance of the police but took to patrolling the streets themselves, photographing the suburban "johns" or plastering their cars with stickers that say they've been seen in an area of prostitution. But the ladies of the evening (and noon and morning) still ply Logan Circle, often in a desperate effort to feed their drug habits.

And the trouble spreads.

First of all, it spreads geographically. The "Mayfair market" used to be a small drug outpost. Now it occupies the entire courtyard of Mayfair Mansions-Paradise Manor, as upwards of 100 dealers, many of them Jamaicans from New York, vend their deadly wares. The longer the drug traffic survives there, the more likely it is to spread to other vulnerable developments.

It also spreads up the socioeconomic scale, sucking more and more nonpoor into the incredibly lucrative drug trade.

And it spreads down the age scale. It is no longer uncommon to see 10- and 11-year-olds working first as sentries to let the dealers know when the police are on the way and then as "runners" to deliver packets of cocaine or its seductive "crack" derivative.

An adolescent who can earn hundreds of dollars a week for a few hours work or who sees older teen-agers driving BMWs bought with drug profits is immune to blandishments of a straight job that pays the minimum wage. Entire neighborhoods are lost already, and entire cities are being threatened.

And nobody knows what to do about it. Desperate suggestions (some of them from me) have run the gamut from mothers' patrols to physical assaults on pushers to legalizing drugs to take the profit out of the traffic.

The suggestions are mostly wishful thinking. The truth is that all of us, no less than the pitiful Blackburns, are vulnerable to the prospect of money-driven criminals taking over our turf. For the sake of our cities, our families and ourselves, we've got to find new ways of fighting back before it's too late.