The operator of the trans-Alaska pipeline received approval to restart the 800-mile (1,300-kilometer) line, three days after a leak was found near a pump station at Prudhoe Bay.

State and federal regulators gave the company the green light late Tuesday afternoon to do what is being described as an "interim restart," said Michelle Egan, spokeswoman for Alyeska Pipeline Service Co., which operates the pipeline.

Egan said the restart will allow some oil to begin flowing again.

The pipeline has been shut down since Saturday at 8:50 a.m. local time, making it one of the longest shutdowns since the line from America's largest oil field went into operation in 1977.

Pipeline pressure was being increased Tuesday night and other preparations were under way for the restart, Egan said.

Alternative pipe had been identified that can be used to get the oil moving again while work continues on a bypass line to go around the pump house leak, Egan said.

Fabricating the bypass pipe was expected to take another four days and an additional 36 hours would be needed for installation, officials said.

The trans-Alaska pipeline delivers about 13 percent of the country's domestically produced oil.

With temperatures dropping on the North Slope, concerns increased Tuesday about the impact of cold on the shut down pipeline. Restarting the pipeline and getting the oil moving also would move a device known as a cleaning pig in the line, officials said.

The concern was that the cleaning pig would push ice and wax from the oil into machinery and damage equipment once the line is permanently restarted. Getting some of the oil moving will allow operators to move the cleaning pig to an area where it can be sidelined and captured, Egan said.

When the leak was discovered Saturday morning, North Slope production was cut by 95 percent. The pump station where oil was found is the last stop for crude before it enters the main line and is delivered to tankers in Valdez for delivery to the West Coast.

Plans called for installing a 157-foot (47-meter) bypass pipe to circumvent the area of the leak, which is in an underground pipe encased in concrete. A small amount of oil continued to drain into the basement of Pump Station 1. As of Tuesday afternoon, about 1,200 gallons (4,550 liters) had been sucked up.

The bypass pipe will connect one of three booster pumps to the main pipeline. An 800-gallon (3,000-liter) containment vault was being built near the pump station.

The Alaska Department of Environmental Conservation said it wasn't known whether oil from the leaky pipe reached the ground. Several groundwater drainage systems around the pump station were inspected overnight and were free of oil.

About 90 percent of Alaska's general fund revenues come from the petroleum industry, and the shutdown is costing the state of Alaska more than $18 million a day in taxes and oil royalties, said Lacy Wilcox with the Department of Revenue.

While that money will begin flowing once the pipeline is restarted, "today it is a loss," she said.

In May, a storage tank at one of the pump stations along the pipeline overflowed, forcing a shutdown that lasted three days, seven hours and 40 minutes. The pipeline's longest shutdown _ again caused by a problem at a pump station _ began on Aug. 15, 1977, a few months after the pipeline went into operation. It lasted four days, 14 hours and 11 minutes.