ALMOST ON AN ANNUAL basis, Washington-area congressmen have been proposing plans for protecting the Potomac River above the nation's capital. Since the C&O Canal park has been established on the Maryland side, the major challenge involves the Virginia-West Virginia shore. Each bill has moved further away from federal control and toward state and local initiatives to temper development and keep the riverside clean and green.

Every effort has failed for the same reason: because key West Virginians have said no. The panhandle people have resolutely opposed any outside intrusion on their domains. Meanwhile, they have done much less than other Potomac basin governments, notably Loudoun County, to safeguard the shoreline themselves. So regional planning remains a dream - and from Harper's Ferry upstream, insensitive development, pollution and recreational boat-jams on the river are still real, dismaying possibilities.

Now, Rep. Joseph L. Fisher (D-Va.) has taken a different tack by introducing a bill that stops at the West Virginia line. It provides for a regional planning effort covering only the Virginia, Maryland and District parts of the river above Key Bridge. That is one way around a political obstacle. But the price is a much-diminished bill, limited to areas where it is less needed because public initiatives have been extensive and cooperative efforts are well advanced.

Mr. Fisher hopes that if a modest local-state-federal program can get started, West Virginians will gradually see how helpful it can be and come around. It's worth a try. Yet successful planning next door may have less influence on the holdouts than pressures on their own turf. And those are mounting. Last year, the National Park Service acquired the old Western Maryland railroad right-of-way that cuts across the Potomac bends above Hancock. That puts a federal path on the West Virginia shore. Meanwhile, Maryland and the Corps of Engineers have been stepping up their regulation of marinas and other projects affecting the river itself. So isolation is no longer a real option for West Viginians; the question now is whether they will abdicate Potomac conservation to others, or take some initiative themselves.