There's no end in sight for the situation in the Gulf of Mexico. Anderson Cooper reports live tonight from the region as BP attempts to stop the leak. Watch "AC360°" tonight at 10 ET on CNN for the latest on stopping the leak.
Venice, Louisiana (CNN) -- BP's much-anticipated attempt to cap its undersea gusher in the Gulf of Mexico, a spill now estimated at twice the size of the Exxon Valdez disaster, was suspended for more than 16 hours before it was restarted late Thursday afternoon, a BP executive said Thursday.
"This whole operation is very, very dynamic," Doug Suttles, the company's chief operating officer, told CNN's "John King, USA."
"When we did the initial pumping (Wednesday), we clearly impacted the flow of the well. We then stopped to monitor the well. Based on that, we restarted again. We didn't think we were making enough progress after we restarted, so we stopped again."
The light-brown material that was seen spilling out of the well throughout Thursday was the previously pumped fluid from the "top kill" procedure mixed with oil, he said.
CNN.com Live: Underwater view of top kill procedure
"I probably should apologize to folks that we haven't been giving more data on that," Suttles said when asked why it took so long for BP to announce it had suspended the top kill. "It was nothing more than we are so focused on the operation itself."
Suttles said part of the problem is that too much mud is leaving the breach instead of going down the well. "So what we need to do is adjust how we are doing the job so that we get more of the drilling mud to go down the well," Suttles said.
He said one solution would be to introduce solids -- known as "bridging material," or its variant "junk shot" -- into the mix.
The revelation that the procedure had gone on a 16-hour break angered local officials and observers. Neither President Obama or Coast Guard Adm. Thad Allen, who is leading the government's response to the oil spill, appeared to be aware of the break when they addressed reporters at separate news conferences Thursday.
Plaquemines Parish President Billy Nungesser, who has been extremely critical of the federal response to the spill, said the delay in information from BP was "par for the course."
"We've been dealing with this from day one, and the information has not flowed on anything," he told CNN's Anderson Cooper.
Douglas Brinkley, a presidential historian at Rice University, agreed, saying, "It's unacceptable to trust BP."
"Whatever they say is meant to minimize situations," he told Cooper. "They haven't been transparent -- they're not honest with people."
A White House official told CNN that people inside the White House knew about the temporary halt in the "top kill," but it wasn't clear if Obama was aware of it.
The official said the president wouldn't micromanage every decision made by BP and government officials working the disaster site. The White House didn't announce the break because it didn't seem to be a major issue -- the operation had continued throughout the break and the pumping of the liquid resumed later in the afternoon, the official said.
"It would have been a bigger deal if the entire operation stopped -- and they want to make that distinction," CNN Senior White House Correspondent Ed Henry reported.
BP officials say the procedure could take another 24 to 48 hours to complete, though whether the top kill will successfully stop the flow of oil is uncertain.
Enormous brown plumes of drilling "mud" billowed from the damaged well during the process, which BP Managing Director Bob Dudley called "a "titanic arm-wrestling match" a mile below the surface.
Allen, who is leading the government's response to the oil spill, earlier said the work "is moving along as everyone had hoped."
"They're pumping mud into the well bore, and as long as mud is going down, hydrocarbons are not going up," Allen told reporters Thursday afternoon. The work could take another night, he told reporters in Venice, near the mouth of the Mississippi River.
"I think we just need to let that run its course, and we will see what happens," Allen said. However, asked about reports the procedure had been halted, Allen said he hadn't talked to BP officials yet.
Stopping the leak took on even more urgency after government scientists released spill estimates that far exceed the previous 5,000-barrel-a-day number given by BP.
The burst well is spewing oil at a rate of at least 12,000 to 19,000 barrels a day, U.S. Geological Survey Director Marcia McNutt told reporters Thursday, meaning 260,000 to 540,000 barrels had leaked as of 10 days ago -- larger by far than the 250,000 barrels spilled when the tanker Exxon Valdez ran aground in Alaska's Prince William Sound in 1989.
The 38-day-old spill was beginning to take its toll on Louisiana's sensitive coastal marshes, where heavy oil has been killing plant life and fouling local wildlife and fisheries. On Thursday, the eve of the Memorial Day holiday weekend, the beaches of Grand Isle were empty.
"If only it gets stopped, if what they did yesterday works, that's the beginning of the end," Grand Isle Tourism Commissioner Josie Cheramie said. "We can clean up what's already been put out there, but we just really need to get it stopped. That's the main thing."
The spill claimed a job in Washington, as the head of the scandal-plagued federal agency that oversees offshore drilling resigned.
Elizabeth Birnbaum stepped down as head of the Minerals Management Service "on her own terms and own volition," Interior Secretary Ken Salazar told a House subcommittee. Two Obama administration sources told CNN that she was fired.
Watch Salazar defend the former director
Reports from the agency's independent inspector general have painted a picture of an agency that has had close ties to the industry, most recently noted in a report on the Lake Charles, Louisiana, office released Tuesday.
Salazar has ordered the agency split into three parts with separate responsibilities since the April 20 explosion on an offshore drilling rig that caused the spill. In a news conference Thursday afternoon, President Obama said the spill shows "more reforms are needed."
"For years, the oil and gas industry has leveraged such power that they have effectively been allowed to regulate themselves," Obama said. He said U.S. laws were "tailored by the industry to serve their needs instead of the public's," giving short shrift to environmental concerns.
Watch Obama talk about the government's role
After a monthlong review of the industry, he announced his administration was suspending dozens of drilling projects, canceling plans to open new parts of the Gulf of Mexico and the Virginia coast to exploration and suspending new deepwater permits for another six months.
Obama also defended his administration's response to the disaster, telling reporters that people who accuse it of being too slow to respond "don't know the facts."
Watch Obama discuss oil drilling reforms
"It doesn't mean it's going to happen right away or the way I'd like it to happen. It doesn't mean that we're not going to make mistakes," he said. "But there shouldn't be any confusion here: The federal government is fully engaged, and I'm fully engaged."
The spill erupted April 20, when the drilling platform Deepwater Horizon exploded and burned about 40 miles off Louisiana. The rig sank two days later, taking 11 of its crew of 125 with it.
The Coast Guard and the Minerals Management Service are leading a joint investigation in Louisiana, while several congressional committees are also investigating the disaster.
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BP, rig owner Transocean and oilfield service contractor Halliburton have all blamed each other for the explosion, which witnesses have said was preceded by a series of unusual pressure tests and a rush of gas out of the well.
One of BP's two representatives on the rig, Robert Kaluza, has refused to testify in the Louisiana hearings, citing his Fifth Amendment right against self-incrimination, the Coast Guard told CNN. The other, Donald Vidrine, bowed out of his scheduled Thursday appearance, citing illness.
The rig's chief mechanic, Doug Brown, testified Wednesday that Transocean and BP managers argued about plans to finish the well on the day of the explosion, with BP's representative winning the argument. He could not identify which of the BP representatives was involved in the dispute, and BP had no comment on his account.
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The rig's offshore installation manager, Jimmy Wayne Harrell, told the Louisiana investigation Thursday that there was no "heated debate." But he said he did reject an initial BP plan to start replacing drill "mud" with seawater without conducting a negative pressure test on the well's initial cementing.
"I told him it was my policy to do a negative test before displacing with seawater," Harrell said. He placed the discussion the day before the blast, and he said Kaluza, the "company man" in the meeting, agreed to add the negative test to the procedure.
Under questioning by an attorney for Halliburton, which did the cementing work to plug the well, Harrell said BP decided not to do a "bottoms-up" test used to measure temperatures and pressures at the deepest part of the well.
Harrell said he wasn't concerned about the lack of a bottoms-up test, but said he wasn't aware that Halliburton had recommended using "substantially more mud" as a counterweight in the drill line than BP had recommended.
CNN's Suzanne Malveaux, Ed Henry, Richard Allen Greene, David Mattingley, Lisa Desjardins and Marylynn Ryan contributed to this report.