District government agencies, which use about 2.5 billion gallons of water a year, have begun readying plans for conserving water against the possibility of a drought and summertime shortages.

In response to a memo from Mayor Walter E. Washington, agencies have begun drawing up plans that range from simple maintenance such as repairing leaky faucets to setting up priorities for where the water would be turned off.

No water shortage is on the immediate horizon, but water planners have said that the drinking water supply is so undependable that the risk of shortages and rationing is real. On a few days every summer water users have taken more water out of the Potomac than it can supply on its very lowest days, but peak demand and minimum supply have not yet converged.

"It looks all right for now, providing we get some rain in the Potomac River basin," said director of water resource management Jean B. Levesque. "If we have an extended period - two or three months of hot weather and no rain - there are going to be some problems."

Although 2.5 billion gallons sounds like a lot of water, it is only about 3 per cent of the 74 billion gallons of water produced in the metropolitan area. If a water shortage develops, a Metropolitan Washington Council of Governments plan allowing for only essential services would go into effect in all jurisdictions, said Levesque.

The use of hoses and sprinklers to water ornamental plants and lawns would be prohibited, as would the use of water to wash motor vehicles, to wash streets and the use of ornamental fountains, said Levesque.

A review of water use by the city recreation department's aquatics division, which uses about 88.3 million gallons of water a year, is an example of the type of review of water usage now underway in the city government.

"Our first line is to conserve water, to cut off all our leaks," said James Tompkins, director of the division which operates the city's swimming pools. The department has inspected shower valves, faucets and other fixtures that could be losing water and inspected pipes as well, he said.

"This winter didn't do us any favors," he said. The types of maintenance now underway include such things as checking to make sure that showers which are supposed to squirt water for 40 seconds and then cut off actually cut off on time.

The next step in tentative plans the acquatics division has developed might be to control more closely when showers are in operation, allowing swimmers to use them at the beginning of an hour, for instance, but not in between times.

"Then you start getting into curtailment of the hours in street showers," said Tompkins. Street showers are fire hydrants with giant shower heads attached, which normally run four hours a day to provide relief from the summer heat for the city's children. Water running into the streets from those "can average about 50 gallons a minute," said Tompkins. "That's one of the first places we would cut back."

Next to go would be small, shallow "walk-to-learn-to-swim" pools. Because the department cannot afford night watchmen, these pools are drained every night and refilled every morning, said Tompkins. Water in larger pools which are guarded is recirculated, with constant monitoring of water quality and small additions to make up for water lost through evaporation or splashing.

Next might come the shutting down of some full-sized swimming pools. "We'd leave one pool in each area in each ward until, if we were pushed to it, we'd close all the outdoor pools," Tompkins said. "I would hope that never happens.