WEST ELIZABETH, PA., JAN. 4 -- Drinking water supplies began drying up in Pittsburgh's suburbs today because of a million-gallon diesel fuel spill that fouled the Monongahela and Ohio rivers, where crews had removed only 30,000 gallons from the surface.

"We have no water in our community," said Sue Jarecki, a clerk for the Municipal Authority of Robinson Township, which serves 13,000 residents.

Water tanks were placed at a school-bus depot and two fire stations where residents could take containers to fill and carry home, she said.

"We could go down . . . at any time," said spokesman Dennis Casey of Western Pennsylvania Water Co., which serves 750,000 people and had to close one of its two water intakes on the Monongahela.

Casey said faucets could run dry before day's end for as many as 50,000 residents of seven communities in Pittsburgh's suburban South Hills who are served by the closed intake.

"The main tank in Greentree is empty. You can go up and tap on it. It's hollow," he said.

Floating booms, placed on the Monongahela after an Ashland Oil Co. tank collapsed Saturday at the company's Floreffe terminal here, trapped the bulk of the oil. But an undetermined amount breached the barriers at Pittsburgh, entered the Ohio River and was detected as far away as Newell, W.Va., 90 miles downstream, Coast Guard spokesman Scott Nelson said. The fuel did not form a continuous slick, he said.

Officials of Western Pennsylvania Water Co. asked customers to conserve water, and water authorities downstream repeated the call to their customers. Schools were closed in seven districts as a water-conservation measure, affecting an estimated 18,000 students.

Gov. Robert P. Casey (D) declared a disaster in Allegheny, Beaver and Washington counties surrounding Pittsburgh, freeing the National Guard to help provide water.

Pittsburgh's water comes from the Allegheny River and was reported to be unaffected. The Allegheny and Monongahela converge near downtown Pittsburgh to form the Ohio River.

The heavily used Monongahela remained closed to river traffic over the 27 miles between the Ashland terminal and Pittsburgh.

Emergency work crews were suctioning the clear, smelly oil from the surface of the river behind the floating booms. About 30,000 gallons had been recovered by today, and officials said the cleanup, which will cost millions of dollars, is expected to continue for weeks.

The Ashland tank was 40 years old and was moved last year from Cleveland. It was put into service at the Ashland terminal in August.

The tank's contents of 3.5 million gallons were unleashed while it was being filled, company spokesman Roger Schrum said. A dike around the tank contained 2.5 million gallons, but the rest washed over the top.

"It rumbled, rumbled, rumbled and then, boom! The tank burst. My wife was looking out the window, taking down the Christmas tree, and all at once the tank disappeared," said Leroy Rogerson, 65, of the Floreffe section of Jefferson Borough.

Company engineers and government regulators are investigating the accident.

"The metal was tested and determined to be of sound strength," Schrum said. "The structural integrity of the tank passed all inspections."

Larry Skinner, whose Skinner Tank Co. of Yale, Okla., moved the tank for Ashland, said the foundation may have shifted because of a leak in an underground water pipe. Authorities said that possibility is under investigation.

Gov. Casey said he invited the governors of Ohio, West Virginia, Kentucky, Indiana and Illinois, which all border the Ohio River, and members of Pennsylvania's congressional delegation to join him in asking the federal Environmental Protection Agency for aid.

"We will be there to help oversee the cleanup and provide technical expertise," EPA spokeswoman Robin Woods said in Washington.