But unlike the agency's drought declarations in 1981 and 1985, today's declaration does not impose mandatory restrictions on water use for the 17 million people who take water from the basin, including residents of New York City, Philadelphia and much of western New Jersey.

Instead, the agency, the Delaware River Basin Commission, issued a milder decree intended to quicken the refilling of the three major reservoirs in the first half of 2002. It ordered that four other reservoirs in the basin share in the requirement, now faced only by the New York reservoirs, to release water to maintain mandated flows in the Delaware River.

The New York reservoirs — the Cannonsville, the Pepacton and the Neversink, known collectively as the Delaware system — have dumped a record 110 billion gallons into the Delaware since June to maintain the flow requirement, said Michael A. Principe, director of the city's bureau of water supply.

In nondrought years, he said, 30 billion to 50 billion gallons of reservoir water is used to augment the Delaware. But he said the 110 billion gallons needed in the latter half of this year has helped drop water levels in the three reservoirs to a record low. When full, the three reservoirs hold about 271 billion gallons and provide about half of the average of 1.2 billion gallons used in New York City each day. Today, the three hold only 63,804 billion gallons, or 23.6 percent of capacity. The previous low, 25.3 percent of capacity, occurred on Feb. 2, 1981, during the drought of 1980-81.

But Mr. Principe said it is unlikely the city will declare an emergency in coming weeks and impose mandatory controls on water use as it did in 1981, because there is little risk now that one of the city's three reservoir systems will dry up, a criterion for a drought emergency. The city's other two systems, the Croton and the Catskills, are about 35 percent full, the commission reported today.

Echoing other water officials at the commission meeting here, Mr. Principe said that if there is an optimum time for a drought it is in winter. Demand for water is far below the highs of summer, and forests absorb far less rainfall now than in June and July.

Mr. Principe also said the city is far better prepared to withstand a drought now, because a 10-year campaign to install water meters and low-flow toilets has cut daily demand by about 200 million gallons since 1991. Since early November, the city has appealed to residents to conserve water.

"The real problem is if the drought continues into next summer," he said. "Then we'll be in trouble."

Mr. Principe said other factors that helped deplete the three Delaware system reservoirs were a 10- inch rainfall shortage in their watershed since summer, and the city's heavier-than-usual reliance on the three reservoirs this year because of repairs to aqueducts in the Croton system in Westchester and Putnam Counties.

Because of their low levels, the three Delaware system reservoirs are supplying only about 35 percent of the city's daily water needs now instead of the usual 50 percent, Mr. Principe said. Use of the Croton system has doubled to about 20 percent of daily needs, and the Catskill system is providing 45 percent instead of the customary 40 percent, he said.

In earlier conservation moves since November, the commission has cut the amount of water the city can draw from the Delaware system to 520 million gallons a day from 800 million, and relaxed its river flow requirement.

The four basin reservoirs now required to help maintain the Delaware River's flow rate are two owned by electrical power companies, the Mongaup in New York State and Lake Wallenpaupack in Pennsylvania, in addition to the Nockamixon, a recreational lake owned by Pennsylvania, and the F. E. Walter Reservoir, a flood-control lake in Pennsylvania owned by the Army Corps of Engineers.