HOUSTON — BP on Thursday night restarted its most ambitious effort yet to plug the oil leak in the Gulf of Mexico, trying to revive hopes that it might cap the well with a “top kill” technique that involved pumping heavy drilling liquids to counteract the pressure of the gushing oil.
BP officials, who along with government officials created the impression early in the day that the strategy was working, disclosed later that they had stopped pumping the night before when engineers saw that too much of the drilling fluid was escaping along with the oil.
It was the latest setback in the effort to shut off the leaking oil, which federal officials said was pouring into the gulf at a far higher rate than original estimates suggested.
If the new estimates are accurate, the spill would be far bigger than the Exxon Valdez disaster in 1989 and the worst in United States history.
Doug Suttles, BP’s chief operating officer for exploration and production, struggled to offer guidance on whether the latest effort was likely to succeed.
“It’s quite a roller-coaster,” Mr. Suttles said. “It’s difficult to be optimistic or pessimistic. We have not stopped the flow.”
President Obama, who planned to visit the gulf on Friday, ordered a suspension of virtually all current and new offshore oil drilling activity pending a comprehensive safety review, acknowledging that oversight until now had been seriously deficient.
His action halted planned exploratory wells in the Arctic due to be drilled this summer and planned lease sales off the coast of Virginia and in the Gulf of Mexico. It also halts work on 33 exploratory wells now being drilled in the gulf.
Mr. Obama said at a news conference in Washington that he was angry and frustrated about the catastrophe, and he shouldered much of the responsibility for the continuing crisis.
“Those who think we were either slow on the response or lacked urgency, don’t know the facts,” Mr. Obama said. “This has been our highest priority.”
But he also blamed BP, which owns the stricken well, and the Bush administration, which he said had fostered a “cozy and sometimes corrupt” relationship between oil companies and regulators at the Minerals Management Service.
The chief of that agency for the past 11 months, S. Elizabeth Birnbaum, resigned on Thursday, less than a week after her boss, Interior Secretary Ken Salazar, announced a broad restructuring of the office.
“I’m hopeful that the reforms that the secretary and the administration are undertaking will resolve the flaws in the current system that I inherited,” she said in a statement.
Mr. Obama plans on Friday to inspect the efforts in Louisiana to stop the leak and clean up after it, his second trip to the region since the explosion of the Deepwater Horizon rig on April 20. He will also visit with people affected by the spreading slick that has washed ashore over scores of miles of beaches and wetlands.
Even as Mr. Obama acknowledged that his efforts to improve regulation of offshore drilling had fallen short, he said that oil and gas from beneath the gulf, now about 30 percent of total domestic production, would be a part of the nation’s energy supply for years to come.
“It has to be part of an overall energy strategy,” Mr. Obama said. “I mean, we’re still years off and some technological breakthroughs away from being able to operate on purely a clean-energy grid. During that time, we’re going to be using oil. And to the extent that we’re using oil, it makes sense for us to develop our oil and natural gas resources here in the United States and not simply rely on imports.”
In the top kill maneuver, a 30,000-horsepower engine aboard a ship injected heavy drill liquids through two narrow flow lines into the stack of pipes and other equipment above the well to push the escaping oil and gas back down below the sea floor.
As hour after hour passed after the top kill began early Wednesday afternoon, technicians along with millions of television and Internet viewers watched live video images showing that the dark oil escaping into the gulf waters was giving way to a mud-colored plume.
That seemed to be an indication that the heavy liquids known as “drilling mud” were filling the chambers of the blowout preventer, replacing the escaping oil.