WASHINGTON - President Obama defensively and sometimes testily insisted yesterday that his administration, not oil giant BP, was calling the shots in responding to the worst oil disaster in the nation's history.

"I take responsibility. It is my job to make sure that everything is done to shut this down," Obama told a news conference in the East Room of the White House. The Gulf of Mexico oil spill dominated the hourlong session.

He called the spill, now in its sixth week, an "unprecedented disaster" and blasted a "scandalously close relationship" he said has persisted between Big Oil and government regulators.

Obama announced steps to deal with the aftermath of the spill, including continuing a moratorium on drilling permits for six months. He also said he was suspending planned exploration drilling off the coasts of Alaska and Virginia and on 33 wells under way in the Gulf of Mexico.

The president's direct language on being in charge of the spill response, which he repeated several times, marked a change in emphasis from earlier administration assertions that, while the government was overseeing the operation, BP had the expertise and equipment to make the decisions on how to stop the flow.

As recently as Monday, the top federal official in charge of dealing with the oil catastrophe, Coast Guard Adm. Thad Allen, declined to broadly say the federal government was "in charge." Instead, when asked about that, Allen told reporters that BP was responsible for the cleanup and the government was accountable to make sure the company did it. "I would say it's less a case of 'in charge,' " Allen said when asked about that phrase.

Yet, with each passing day, public frustration with Obama's administration has grown, and his poll numbers on the matter are dropping.

Claiming control carries its own political risks for Obama, because any failure to stop the gusher will then belong to him.

He could suffer politically if his administration is seen as falling short of staying on top of the problem or not working hard to find a solution.

"The American people should know that from the moment this disaster began, the federal government has been in charge of the response effort," Obama said. He was reacting to criticism that his administration has been slow to act and has left BP in charge of plugging the leak.

Obama said many critics failed to realize "this has been our highest priority."

"My job right now is just to make sure everybody in the Gulf understands: This is what I wake up to in the morning, and this is what I go to bed at night thinking about. The spill."

"There shouldn't be any confusion here. The federal government is fully engaged," he said, underscoring his central point.

Asked about inevitable comparisons between his handling of the disaster with his predecessor's handling of Hurricane Katrina in 2005, Obama said: "I'll leave it to you guys to make those comparisons and make - and make - and make judgments on it, because - because what I'm spending my time thinking about is how do we solve the problem?

"And I'm confident that people are going to look back and say that this administration was on top of what was an unprecedented crisis," he added.

"This has been our highest priority," he said. He conceded that "people are going to be frustrated until it stops."

Over and over, the president sought to counter criticism that the administration was giving too much leeway to BP PLC. "Make no mistake, BP is operating at our direction," he said.