At 3:36 p.m. last Thursday in Atlanta, an alarm sounded in the space-ship-like control room from which operators run the giant Colonial petroleum pipeline that carries gasoline and oil 1,675 miles north from refineries in Houston to the industrial flats of New Jersey.

Seven-hundred-fifty miles northeast of Atlanta, an unmanned and abscure pumping station at Conowingo, Md., on the banks of the Susquehanna River, had shut itself down and announced the fact via remote control to Atlanta. Reason: unknown.

During the next two minutes, the controllers in Atlanta made blunders that caused the pipeline to burst south of Washington, polluting rivers, threatening the water supplies of hundreds of thousands of people, nearly causing a gasoline shortage in the Washington area, and raising serious questions here and nationally about the safety of the nation's 27,000 miles of oil pipelines.

"I'm terribly nervous," Fairfax County Supervisor Audrey Moore said yesterday. "I don't feel at all comfortable with the knowledge that Fairfax County is crisscrossed by petroleum pipelines."

Colonial and another major pipeline called Plantation -- both owned by the major oil companies -- run through Fairfax County, delivering 90 percent of the Washington area's gasoline, heating and commercial oil and aviation fuel. The pipelines run underground.

As oil cleanup efforts continued yesterday on the Occoquan River near Manassas and on the Rappahannock River upstream of Fredericksburg, Fairfax Board of Supervisors Chairman John F. Herrity announced that Colonial executives will be called before the board to answer some "serious questions."

On Tuesday, Virginia Gov. John N. Dalton declared a state of emergency in the polluted Occoquan watershed and in Fredericksburg, where water conservation measures are in effect.

The instant the alarm buzzer sounded in Atlanta last Thursday, the attention of the operators in Colonial's control room was riveted on the dials and moving graphs monitoring the giant pipeline system.

According to Colonial spokesman James Sorrow, the dials told this tale:

As soon as the big electric-driven pumps at the Conowingo station shut down, the vast quantity of oil in the 32-inch diameter pipe began to slow down from its normal pace of about 5 miles an hour.

Because the pipeline was full -- one "batch" of oil or gasoline pushing along another all the way from Houston -- and because the liquid cannot compress like natural gas, the slow-down began to exert enormous pressures on pump stations back down the line and on the .281-inch-thick treated steel pipe itself.

One by one the pump stations back down the line -- Aberdeen, Baltimore, Dorsey Junction -- began automatically shutting down, as they are programmed to do by their computers in such a situation.

As the seconds ticked past, the pressure exerted by the gasoline and oil flowing past these pumping stations at more than 18,000 gallons a minute quickly reached the breaking point.

The way Sorrow tells it, the disaster still could have been averted at this point had it not been for human error by a controller in Atlanta.

"He made a choice which turned out to be a very poor one," Sorrow said. "He could have then activated a computer program which would have resulted in an orderly shutdown of the northern portion of the entire system. But he did not."

Instead, the operator sought by remote control to increase the flow from the main pipeline into a 22-inch stub line that runs east into the center of Fairfax City, where giant storage tanks operated by Amoco, Texaco, Gulf and Cities Service could have received the overflow and eased the pressure on the main pipeline.

It didn't work. The stub line could not take enough oil quickly enough to relieve the pressure. Suddenly the dials in Atlanta showed that the pressure on the entire system had eased dramatically: there was a break in the line.

"He knew he had brought the farm right there," said Sorrow. "It all happened in less than two minutes."

The Atlanta controllers could tell approximately where the break was, but they did not know the precise location nor did they know if there was one break or several.

At about 3:40 p.m. -- four minutes after the whole incident began -- people noticed oil on the roadway near Rte. 234 and Sudley Manor Drive in Manassas. They called police, and by 4 p.m. police had found a geyser of oil coming from the group nearby.

In Atlanta, operators furiously worked the system to stop additional oil from moving toward the break area and to speed up its movement to the north. Then they shut down the entire piepline, and it remained closed until Monday morning.

By the time it was all over, 200,000 gallons of aviation kerosene intended for commercial airliners had polluted the headwaters of the Occoquan River near Manassas. In Fredericksburg, 34 miles to the south, 60,000 gallons of No. 2 home heating oil spilled into the Rappahannock upstream of the city.

The second spill went undetected for almost 24 hours while officials fought the larger rupture. During that time the pollution spread extensively, making it more difficult to contain.

Yesterday, workers had recovered much of the oil and contained the rest. Officials said the crisis is nearly over.

But the questions remain.

Colonial is considered a modern, well-managed company with its pipes only 18 years old, and federal environmental officials consider pipelines a relatively safe way to move oil -- certainly safer than ships.

But the U.S. Department of Transportation which regulates pipeline safety, has only 16 inspectors for the entire country, and they must inspect natural gas and other pipelines as well as oil pipelines. The states help in some cases, but Virginia has refused to help inspect the oil pipelines on grounds that it lacks the personnel.

The federal inspectors examine Colonial's maintenance records once a year, keeping to that pace even though the company experienced a large spill similar to the current one in North Carolina last year, according to Sorrow.

Fairfax County Supervisor Marie Travesky summed up by feeling on the Board of Supervisors yesterday by saying she was 'really concerned "because Colonial only last week received approval from the board for a pipeline extension in the county.

"They will have to answer a lot of questions before that pipeline goes through Fairfax County now," she said.