However, an official from BP PLC, which leases the rig, said he did not believe the newly discovered leak has increased the amount of oil spilling into the water beyond earlier estimates. Coast Guard Rear Adm. Mary Landry disagreed with his statement at a news conference and said she was relying on a new estimate from the National Oceanic Atmospheric Administration.
She said NOAA experts now estimate that 5,000 barrels a day of oil are spilling into the gulf. Officials had estimated the leak for days at 1,000 barrels a day.
The news came hours after crews tried a test burn on the massive spill to try to slow it from reaching the U.S. shoreline.
Doug Suttle, chief operating officer for BP, said he thinks the estimate of 1,000 barrels a day is accurate. He showed a diagram showing where the leaks are and said the newly discovered leak is upstream from the previous leaks.
"Due to its location, we do not believe this changes the amount currently believed to be released," he said.
When asked again, Landry stuck to the NOAA estimate and said it was based on aerial surveys, study of the trajectory of the oil slick and other factors.
The Secretary of Homeland Security has briefed President Barack Obama on this new information and the government has offered to have the Department of Defense help contain the spill and protect the shoreline and wildlife, she said.
"It has become clear after several unsuccessful attempts to determine the cause" that agencies must supplement what's being done by the company, she said.
Crews late Wednesday afternoon started a test burn on the massive spill, which Landry noted was successful. Rig operator BP PLC had planned to continue the oil fires after the test, but as night fell, no more were lit. The burns were not expected to be done at night. No details about when more fires would be lit were mentioned during the late night news conference.
Crews planned to use hand-held flares to set fire to sections of the massive spill. Crews turned to the plan after failing to stop a 1,000-barrel-a-day leak at the spot where a deepwater oil platform exploded and sank.
A 500-foot boom was to be used to corral several thousand gallons of the thickest oil on the surface, which will then be towed to a more remote area, set on fire, and allowed to burn for about an hour.
They had estimated about 42,000 gallons of oil a day was leaking into the Gulf from the blown-out well drilled by the Deepwater Horizon oil rig. Eleven workers are missing and presumed dead. That would be closer to 210,000 gallons a day with the new estimates. The cause of the explosion has not been determined.
Greg Pollock, head of the oil spill division of the Texas General Land Office, which is providing equipment for crews in the Gulf, said he is not aware of a similar burn ever being done off the U.S. coast. The last time crews with his agency used fire booms to burn oil was a 1995 spill on the San Jacinto River.
"When you can get oil ignited, it is an absolutely effective way of getting rid of a huge percentage of the oil," he said. "I can't overstate how important it is to get the oil off the surface of the water."
The oil has the consistency of thick roofing tar.
When the flames go out, Pollock said, the material that is left resembles a hardened ball of tar that can be removed from the water with nets or skimmers.
"I would say there is little threat to the environment because it won't coat an animal, and because all the volatiles have been consumed if it gets on a shore it can be simply picked up," he said.
Authorities also said they expect minimal impact on sea turtles and marine mammals in the burn area.
A graphic posted by the Coast Guard and the industry task force fighting the slick showed it covering an area about 100 miles long and 45 miles across at its widest point.
"It's premature to say this is catastrophic. I will say this is very serious," said Coast Guard Rear Adm. Mary Landry.
From the air, the thickest parts of the spill resembled rust-colored tentacles of various thickness. The air was thick with the acrid smell of petroleum.
Amid several of the thicker streaks, four gray whales could be seen swimming in the oil. It was not clear if the whales were in danger.
More than two dozen vessels moved about in the heart of the slick pulling oil-sopping booms.
Earlier Wednesday, Louisiana State Wildlife and Fisheries Secretary Robert Barham told lawmakers that federal government projections show a "high probability" oil could reach the Pass a Loutre wildlife area Friday night, Breton Sound on Saturday and the Chandeleur Islands on Sunday.
As the task force worked far offshore, local officials prepared for the worst in case the oil reaches land.
In Plaquemines Parish, a sliver of Louisiana that juts into the Gulf and is home to Pass a Loutre, officials hoped to deploy a fleet of volunteers in fishing boats to spread booms that could block oil from entering inlets.
"We've got oystermen and shrimpers who know this water better than anyone," said Plaquemines Paris President Billy Nungesser. "Hopefully the Coast Guard will embrace the idea."
But there was anxiety that the Gulf Coast was not prepared for the onslaught of oil.
"Our ability to deal with this would be like us having a foot of snow falling in Biloxi tomorrow," said Vincent Creel, a spokesman for the city government in Biloxi, Miss. "We don't have snow plows, and we're not equipped to deal with this."
The parish's emergency manager planned to meet in Houma on Thursday with a Coast Guard official to discuss whether volunteers can help, Nungesser said.
"We don't want to just sit by and hope this (oil) doesn't come ashore," Nungesser said.
The decision to burn some of the oil came after crews operating submersible robots failed to activate a shut-off device that would halt the flow of oil on the sea bottom 5,000 feet below.
BP says work will begin as early as Thursday to drill a relief well to relieve pressure at the blowout site, but that could take months.
Another option is a dome-like device to cover oil rising to the surface and pump it to container vessels, but that will take two weeks to put in place, BP said.
Winds and currents in the Gulf have helped crews in recent days as they try to contain the leak. The immediate threat to sandy beaches in coastal Alabama and Mississippi has eased. But the spill has moved steadily toward the mouth of the Mississippi River and the wetland areas east of the river, home to hundreds of species of wildlife and near some rich oyster grounds.
The cost of the disaster continues to rise and could easily top $1 billion.
Industry officials say replacing the Deepwater Horizon, owned by Transocean Ltd. and operated by BP, would cost up to $700 million. BP has said its costs for containing the spill are running at $6 million a day. The company said it will spend $100 million to drill the relief well. The Coast Guard has not yet reported its expenses.
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Associated Press writers Janet McConnaughey, Michael Kunzelman in New Orleans, Melinda Deslatte in Baton Rouge and Holbrook Mohr in Jackson, Miss., contributed to this report.
