“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.