BEFORE HE BECAME mayor, Barry was not exactly in the forefront of any regional cooperation efforts in this area. On the contrary, he confined himself too narrowly, in our view, to the particular needs of the District of Columbia, often casting the suburbs as opponts of the District's interests.So it is reassuring to find some early signs of a change in Mr. Barry's attitude, a suggestion of a greater understanding on his part of the interdependence of the various jurisdictions that make up the Greater Washington area. In his inaugural address, he included a promise to "work to achieve a new unity within the region." More recently, his new administration has been reaching out to befriend its neighbors -- for practical as well as diplomatic purposes.

Area interdependence covers a wide range of common interests. It begins, of course, with Metro -- the classic challenge to intergovernmental relations around here. But District officials have also been talking with their counterparts in Prince George's County about how to handle important sewage problems. And the mayor paid a call on Maryland Gov. Harry R. Hughes, too, not only to talk about congressional representation for the District, but also to establish a working relationship for dealing with any other matters of joint concern that may come up.

None of this erodes any authority of the District of Columbia or diminishes the need for it to seek increased powers of self-government. On the contrary, there is solid evidence that the maintenance of strong ties between the District and its neighbors is more productive in the long run than unilateral decision-making, which often results in hard feelings and, in some instances, retribution.

In the nearly 22 years since political leaders in the Washington area first sat down together to discuss their common problems, the Council of Governments has become one of the most respected and wellstaffed regional organizations in the country. It also happens to be the official metropolitan clearinghouse for the awarding of federal grants in this region -- for roads, airports, mass transit, hospitals, libraries, criminal-justice planning, comprehensive health plans, neighborhood development, open space and water and sewer facilities. Whatever the goals of the new District administration -- getting jobs for the jobless, finding places for low-income families to live or developing regional tax policies -- the results are likely to hinge on the degree to which Mayor Barry expands and reinforces his first efforts to develop practical and productive relationships with the District's neighbors.