* Vote postponed as commission considers new rules
* Environmentalists say delay is victory against drillers
NEW YORK, Nov 18 (Reuters) - A key vote scheduled for Monday to lift a natural gas drilling ban in the Delaware River Basin was postponed on Friday as a commission overlooking water supply in the region remained undecided about opening it up to drillers.
The Delaware River Basin Commission (DRBC), which regulates water use across the 14,000 square mile (36,260 sq km), gas-rich basin, suspended Monday's vote amid speculation that its five members did not have the three votes needed to allow drilling.
"There are still some open issues that the commissioners have to work through," said DRBC spokesman Clarke Rupert, who had no new date for the vote.
Earlier this month, the DRBC proposed ending the drilling moratorium in the basin that stretches across parts of Pennsylvania, New York, New Jersey and Delaware and sits atop the country's biggest natural gas deposit: the Marcellus Shale.
Under proposed new regulations, the DRBC said that it will provide water for no more than 300 natural gas wells over 18 months, at which point they will reassess the rules.
But concern that fracking, the drilling technique that extracts gas from shale by pumping chemical-laced water into rock underground, contaminates water supplies has led to opposition to drilling in the area which provides water for millions of homes across four states.
Environmentalists called the vote delay a victory against fracking.
"The postponement of the DRBC vote on natural gas development regulations is a victory for clean drinking water," the New Jersey Sierra Club. "The vote was to take place on Monday but was delayed as the measure did not have enough votes to pass," it said.
The DRBC declined to comment on the voting.
The five commission members are the governors of the basin states and the commander of the U.S. Army Corps of Engineers' North Atlantic Division, who represents the federal government.
New York, which has its own drilling ban in place, has intimated that it will vote against opening the basin to drilling, as has Delaware, while Pennsylvania is all for it. It is unclear which way the Army Corps and New Jersey will vote. (Reporting by Edward McAllister; Editing by Marguerita Choy)