Ribbons of foul-smelling aviation kerosene from a 250,000-gallon pipeline spill in Manassas coated a 10-mile stretch of Bull Run yesterday, creating what a federal official called "a potentially horrendous situation."

Environmental Protection Agency spokesmen, disavowing earlier statements by local officials that the spill constitutued no health hazard, said the kerosene has the potential to contaminate the Occoquan Reservoir, source of drinking water for 660,000 Northern Virginians.

Officials also are "very concerned" about possible damage to fish and wildlife, one spokesman said.

The leak occurred Thursday afternoon after a 32-inch underground pipe owned by the Colonial Pipeline Co. burst at a Manassas fuel depot. The pipeline is a major petroleum transmission route stretching from Texas to New Jersey.

"In a stream bed this size, a spill of these proportions is just horrendous," said Tom Massey, onscene coordinator of a 25-member EPA team overseeing containment and recovery efforts.

Meanwhile, an undetermined amount of fuel oil spilled into the Rapidan River near Culpeper County, Va., yesterday after another section of the same pipeline sprung a leak.

The oil was reported flowing downstream toward the Rappahannock River, which provides the water supply for the city of Fredericksburg.

Efforts were under way last night to contain the oil by placing a boom across the Rappahannock upstream of Fredericksburg.

Calling the two leaks in a brief period a "million to one coincidence," a Colonial spokesman said early today that the cause of yesterday's leak was not yet unknown. "We've got a lot of investigating to do," he said.

Although the exact amount of oil that leaked yesterday from the pipeline in Burrs Hill, Va., was not known, Colonial official Hal Melendy estimated that it was "not nearly as large" as the Manassas spill.

Estimates of the size of the Manassas leak, put at 100,000 gallons by local officials Thursday, were more than doubled yesterday by EPA.

By 5:30 p.m., the spill had reached several barriers of floatation collars stationed at Bull Run Marina, roughly 10 miles from the intake ducts of the Occoquan Reservoir, in Southern Fairfax County, according to EPA spokesman George V. Bochanski Jr.

Officials and workers at the scene differed on how effective the collars might be in stopping the flow of the pale yellow, oily kerosene. EPA officials, calling the kerosene extremely toxic, said it was impossible to estimate how much already had entered the water table.

Kerosene could reach the Occoquan Reservoir sometime this weekend if the collars fail to block it, EPA said. In that event, the agency said it would recommend that intake ducts be closed temporarily.

Spill recovery workers from a private Baltimore firm, J and L Industries, Inc., erected floatation collars made of absorbent cotton at four stations along Bull Run, according to J and L superintendent Frank Enos. The collars are capable of absorbing 10 times their weight in oil.

"But the currents were very swift. It's like a river in some places," said Fairfax County Fire and Rescue Services Chief George M. Alexander. "The kerosene would thicken at the collar site and eventually begin to flow under them."

Eleven Fairfax County firefighters, wading a chest-deep water to help attach the collars Thursday night, sustained chemical burns from the kerosene, said Fairfax County fire spokesman Stephanie Hoover.One of them, 27-year-old Robert Clark, was treated for burns at Commonwealth Doctor's Hospital before being released.

The collars, and a crude dike of blankets and chicken wire fences erected Thursday at Bull Run Park, managed to contain some of the kerosene. e

"On a warm day like today, a gallon of oil can spread 200 or 300 feet." Enos said yesterday while rubbing bloodshot eyes after being up all night. "It's a mess, really. It's real thin kerosene, and the thinner it is, the quicker it moves."

Enos said he was convinced the spill would go no further than Bull Run Marina where five of the floatation collars and a vacuum "skimmer" with a truck capable of holding more than 5,000 gallons was stationed.

"It ain't going no further than here," Enos said. "We've got people from Newport News and Baltimore here on this and some of them are adding more collars further up. The water level is down about a foot from yesterday and a lot of it is covering the banks."

Colonial spokesman Jim Sorrow said his company will assume the entire cost of the clean-up operation.

"We have no idea why the line broke," he said. "We haven't been able to see the hole yet because we haven't reached it. It was 18 feet deep at that point and there are several large rocks that must be removed."

Sorrow said the pipeline normally moved about "26,000 barrels per hour and there are 42 gallons in a barrel."

"It's impossible to estimate when the pipeline can be restored," Sorrow said. "But it will not cause an immediate fuel shortage in the North.That kerosene is used in domestic aircraft and there is normally a five-day reserve maintained for emergency situations."

Bochanski, the EPA spokesman, said the suburban Washington area's "scientific community has been canvassed" in order to assess the potential damage to the environment. Massey said the EPA was "very concerned about the possibility that (the kerosene) will get into the drinking water . . . it's very toxic."

Ernie Watkins, a representative of Virginia's State Water Control Board, told reporters he would be meeting with other officials to determine a number of contingency plans for getting drinking water if the Occoquan is contaminated.

Fairfax County recently bought a large rock quarry next to the reservoir that will be filled with water to act as a reserve in cases of emergency, but it will not be available soon, a Control Board representative said.

Officials said they could also get fresh water in limited amounts from Fairfax County lakes, and that Arlington County and Falls Church could also furnish drinking water.

A long-range plan to develop intake ducts on the Potomac River to supply Northern Virginia will not be completed until 1981, a Fairfax water authority official said.

Even after the spill has been cleared, Bochanski said environmental investigations to assess the long-run damage to wildlife and the environment will continue. "Some will get by the marina. Officials will be trying to determine what wildlife has been affected and in what ways, like a before-and-after comparison," he said.