THE WATER problem in California is being described as one of drought. It's more than that. In California, where a ninth of the U. S. population lives, before there was a drought there was already a water shortage. The megastate has used up much of its ground water, and even in normal times there are more dippers in the surface water than there is safe supply.

Both the desert civilization of southern California and desert agriculture of the Central Valley that is the state's spine depend on diversions of water from the north -- mainly mountain streams that come together in San Francisco Bay. The diversion to make the southern and central environments hospitable had begun before the drought to threaten the environment -- the San Francisco delta, for example -- to the north.

California is not alone in having such a shortfall. Its difficulties are emblematic of a problem found throughout the arid West and increasingly in parts of the East as well. In Arizona, Tucson faces a finite water supply; in Colorado, the water issue may limit Denver's development; in northern Texas and Oklahoma, the agriculture of an entire region is threatened by the depletion since World War II of the Ogallala aquifer. Fast-growing Florida has serious problems of quality as well as supply of both ground and surface water. These have been accentuated again by drought, and restrictions are in effect in much of the state. The big cities of the East -- New York, Philadelphia, Boston -- have all been involved in intermittent fights for reaching into nearby river basins for water. The Virginia General Assembly, reacting in part to heightened competition for water in the Tidewater region, passed new permitting legislation in 1989 to help in managing surface water supplies. (Maryland, on the other hand, is said to have had provident legislation for years.)

Traditionally, water use has been left to state and local governments to discipline, but there is a federal role as well. The problem is national, and particularly in the West, the federal government is a major water supplier. The government is involved in water quality, which increasingly impinges on supply. Agriculture, a large and often wasteful user, is critically affected by the availability of water; so are those sectors of the economy and parts of the environment, such as wetlands, for which the federal government is responsible.

As with oil, so with water; it ought to be national policy to encourage conservation, but no national policy exists. In California, the Bush administration has been urged to reduce on environmental grounds the subsidized water it sells to agriculture, the largest consumer in the state. It has claimed it lacks the power and has kicked the problem to the courts and the state. The country needs a clearer approach to so precious a resource.