THE TERROR endured by George and Lillian Blackburn, elderly residents of Washington's inner city, during the past year almost surpasses belief. As detailed last Wednesday by staff writer Joseph D. Whitaker, the Blackburns, who get their only income from Social Security, were repeatedly robbed and beaten by neighborhood teen-agers, two of whom even took to sleeping overnight in the couples' small apartment, threatening to kill them if they sought help. The Blackburns, alone, kept silent until a friend accidentally discovered their plight. The predators left the Blackburns without gas or electricity and finally, completely destitute. In April, they broke Mrs. Blackburn's right leg.

In Washington, as elsewhere, crimes against the elderly tend to be statistically insignificant, although many elderly victims don't report crimes for fear of retaliation. But the physical frailty and, often, the economic vulnerability of the victims give crimes against them a particularly devastating effect, even when no force is used.

Many things can be done to reduce the risk and the fear of crime for elderly people. Washington's police department should consider increasing foot patrols and decoys to areas where a pattern of attacks on the elderly has been noted. Police should also continue advising citizen groups on crime-prevention techniques. Local utility companies, with customer permission, could offer to notify a friend or some other third party if a customer's bill is seriously overdue so that that person could contact the customer. Such a notice, if the Blackburns had subscribed to it, might have spared them month of terror. The Washington Gas Light Company offers this service free to all customers.

Elderly people should vary their routine, so that thieves won't know when they're going shopping or to the bank. They should avoid traveling alone, carry only small amounts of cash, and use well-lighted streets. They should get a bank checking account and have the Social Security Administration mail their checks directly to that account, as it does for over 7 million recipients. And they should arrange to have a relative or friend contact them regularly.

Federal, state and local governments now sponsor efforts by community organizations to offer elderly people a variety of services, such as escorting them to banks or stores, installing locks on doors and windows, telephoning them on a regular basis and in other ways trying to make them feel more a part of the neighborhood. Such efforts at the neighborhood and block level, it seems to us, are crucial. For regardless of the amount of outside help, community residents have to take it upon themselves to supply for the elderly their first line of defense.