Officials in Newark, N.J., scrambled to find new sources of water yesterday after two broken water mains spilled more than 75 million gallons outside the city, cutting off half of Newark's regular water supply for at least a month.

Local and state officials differed on whether vandals had caused the break by opening a valve on the pipeline, which usually carries 75 million gallons a day about 28 miles from the Pequannock watershed in Morris County to the Newark area.

Doug Eldridge, spokesman for Mayor Kenneth Gibson, said the city was using a backup reservoir, which holds about an eight-day supply of water. By late yesterday, Eldridge said, the city was to begin drawing on three other area reservoir systems.

Repairing the 1,000 feet of ruptured steel pipes will cost more than $1 million and take at least a month, he said.

"All this water we're going to have to buy, so this is going to be an expensive proposition," Eldridge said. "How much, we don't know yet."

Gibson declared a water emergency, prohibiting Newark residents from washing cars, watering lawns and using water for other nonessential activities.

Gibson also appealed to residents in Wayne, Bloomfield and Belleville, communities that get their water from Newark, to conserve water.

The break occurred about 4:30 a.m. when a concrete blockhouse containing valves collapsed, severing two 48-inch-diameter pipes about 20 miles northwest of Newark in Pequannock Township. The resulting flood carved a canyon "100 feet across, 120 feet deep and a quarter-mile long . . . a miniature Grand Canyon," Pequannock Police Chief Belwin Harper said.

Harper said the flood deposited six feet of mud and rubble on an open field and on the driveway of a home in the sparsely populated Mountainside Park area of Morris County. No injuries were reported.

Harper said he thought a leaking valve had caused the rupture. "We don't know if it's vandals," he said.

But Dan Berardinelli, manager of the Newark water system, said he is "absolutely positive" that vandals lifted a manhole cover to break into the small, partially buried blockhouse. He said vandals must have turned an eight-inch valve, opening the twin pipeline.

A local resident heard the rushing water and called police about 3:15 a.m. Two city water officials turned off the valve when they arrived about 4:30 a.m. and then climbed atop the flooded blockhouse, Berardinelli said.

"As soon as they closed it, the vault gave way," he said. "They had to jump off. They were lucky they weren't killed."