Coast Guard officials said yesterday that a jet fuel storage facility on the Anacostia River may be the source of the oil spill that has coated dozens of ducks near Fort McNair.

Coast Guard investigators yesterday collected samples of jet fuel from the facility, owned by Piney Point Industries, as well as from Delta Air Lines, which is also a possible source, Lt. William Diaduk said.

A Delta 727 that lost power after taking off from National Airport last Wednesday dumped three tons of fuel from an altitude of about 2,000 feet before returning to the airport for an emergency landing.

On the same day, an unspecified amount of jet fuel was transferred between a barge and an oil tank at the Piney Point facility, Diaduk said.

Laboratory analysis of the samples will determine if fuel from either source matches the oil slick, which has weakened and disoriented mallards in the Potomac by stripping their feathers of natural oils.

Delta and airline industry officials yesterday defended the pilot's decision to jettison the fuel, calling it a standard safety practice designed to reduce the weight of the aircraft on the landing gear and to minimize the danger of explosions or fires.

The unidentified captain of Flight 415 did "exactly what he was supposed to do," said Jim Lundy, a Delta spokesman, adding that Delta believes the fuel dumping had nothing to do with the slick.

The oil was found floating on the Potomac River during the weekend and has moved up the Anacostia to spot just north of the Frederick Douglass Memorial Bridge. The blue-green sheen, with its kerosene-like smell, measured about 100 feet long and stretched across the Anacostia yesterday, Diaduk said.

Samples of oil can be identified precisely by their chemical structure, which serves as a sort of fingerprint. The Delta aircraft carried JP 5 jet fuel, while the Piney Point transfer involved JP 4, a lighter grade that evaporates faster, Diaduk said.

The results of laboratory tests could take days to weeks. "There's no reason to rush. The ducks need to be located and cleaned, but they don't care what the source" of the spill is, Diaduk said.

If neither the Delta nor the Piney Point samples match the oil slithering along the Anacostia, the Coast Guard will continue looking at other possible causes. The slick could have been caused by a boat pumping bilge into the water or someone on land pouring kerosene into a storm drain, he said.

"There are lots of possible sources in that area," Diaduk said. "It's not unusual to smell a kerosene-type smell on the Potomac."

If a source is identified, it could be liable for fines for violating a federal law prohibiting any dumping of petroleum products in navigable waters.

The source also could be liable for damages or cleanup costs -- if the spill can be cleaned. As of yesterday, the oil slick was too thin to be cleaned, Diaduk said. "As a practical matter, it's considered uncleanable." He said he expected the oil to dissipate within a few days.

Delta officials said that Flight 415, bound for Dallas-Fort Worth, jettisoned its fuel shortly after 6 p.m. Wednesday and that the fuel should have evaporated before reaching the ground.

In addition, a 10-to-12-knot wind from the southeast would have blown the fuel away from the river, said Lundy, the Delta spokesman. "It was extremely unlikely that the fuel release had any adverse impact on the environment," he said.

Dumping jet fuel to ensure a safe landing is "standard practice if you have to land under emergency conditions," said James F. McCarthy, a spokesman for the Air Transport Association, an airline industry group. "The less fuel aboard the better."

Dumping fuel is recommended during emergency landings, but is also a relatively rare occurrence.

James Wilding, general manager of the Metropolitan Washington Airports Authority, which operates National and Dulles International, said fuel dumping has not been a problem in the region.