IS THIS REGION heading into a long spell of little rain and water shortages? Nobody knows, but every sunny day makes area officials worry more about water supplies. Thus it was heartening to learn, from a staff paper presented last week to the Council of Government's Water Resources Planning Board, that the region may be able to ward off water crises without building more dams or drawing on the estuary's still-polluted supply. According to engineer Daniel P. Sheer, existing reservoirs plus the Bloomington Dam can store enough water to cope with any foreseeable drought until at least the year 2000.

This sounds terribly simply - but there's a big catch: The region's water-supply structure would have to be thoroughly reorganized. The reservoirs (Occoquan and Goose Creek in Virginia and the Paxtuxent dams in Maryland) are not now connected with the systems that provide Potomac water to the District, Arlington, Falls Church and much of suburban Maryland. Miles of large pipelines would have to be laid, at no small cost. Some purification systems would probably have to be modified. Moreover, a new approach to reservoir management would be required. Mr. Sheer suggests, essentially, that areas not now using the Potomac should do so to some extent when the river is high, so that the reservoirs can be kept full for everybody's benefit when the river is low.

The engineering and financial intricacies involved are being studied by several agencies now. The largest challenge, however, will be political. Before the water systems can be connected, the area's governments and the Corps of Engineers will have to get together on a regional water-management plan. Such an accord may sound unlikely at best to anyone familiar with the years of squabbling over sewage treatment and the current discussions about allocating Potomac water during shortages. The underlying point of the COG paper, though, is that the basis of these negotiations should be changed. Instead of quarreling about Potomac water or Patuxent water or water from any one source, area leaders should start looking at all the streams and reservoirs as potential resources for everyone.

That's absolutely right. No city or county should take the risk of assuming that its own supplies are going to be adequate. Interconnections and coordinated management may not avert all water shortages here for the next quarter-century, but they would certainly help. And we would be willing to bet that if area governments do not pool their water, some sunny morning some part of the region is going to wake up very independent - and very dry.