IF REP. HERBERT E. HARRIS'S meeting with Virginia officials and the Corps of Engineers yesterday is any guide, Fairfax County may not get direct access to Potomac River water for some time. County officials are increasingly anxious to tap the Potomac, and perhaps a major tributary , the Shenandoah too. The Corps, however, wants a regional agreement first on how to parcel out the water when the river's flow is low. Right now the engineers are even being vague about how soon the environmental-impact statements could be done. Meanwhile, some members of the State Water Control Board have started to talked about perhaps suing the Corps for the water that they maintain Virginia is legally entitled to.

It is easy to understand both the Virginia's impatience and the Corps amxieties. We think, however, that a plan could be worked out to give Fairfax County a lot of Potomac water without jeopardizing daily supplies of the Corps' customers in the District, Arlington and Falls Church. The key point is that the Corps' Washington Aqueduct system can store only a single day's water supply - but the suburbs have major reservoirs nearby. Thus the suburbs could use and store Potomac water when the river is high, and reserve their reservoirs for times of drought when the Corps would need much of the river's flow.

If larger connections between the region's systems are built, as engineer David Sheer and others have suggested, the Corps could also draw on the reservoirs in case of a record drought or a disaster such as a major fire or toxic spill. The Corps tends to shrugged off this possibility - after all, it hasn't happened yet - but buying some insurance through better interconnections would be prudent.

In short, we think the river and the reservoirs can supply water enough for everyone. What's needed is more political statemanship. Rep. Harris has been trying hard, but Fairfax Board Chairman John Herrity, for one, thinks that a summit conference involving the Secretary of the Army, Gov. Mills Godwin, Acting Gov. Blair Lee and Mayor Walter Washington will be required. He may be right. It's certainly worth a try. At minimum, such a meeting would be less distruptive than suing the Corps, which strikes us as one of the least productive routes that Virginia could take. A serious legal battle could stall Fairfax County's proposed intake for years. Gov. Godwin would be much better advised to intensify the negotiations.Since the elements of the sound, lasting settlement seem to be there, a high-level conference could be a real regional get- together this time.