Washington ? Thrown on the defensive, President Barack Obama acknowledged his administration could have done better in dealing with the biggest oil spill in the nation’s history and misjudged the industry’s ability to cope with a worst-case scenario. Obama will make his second tour of the battered Gulf Coast today.

“I take responsibility. It is my job to make sure that everything is done to shut this down,” Obama declared in a lengthy news conference at the White House on Thursday. As he spoke, well owner BP struggled anew to plug the blown well that exploded five weeks ago, killing 11 workers and sending millions of gallons of polluting oil gushing out.

Obama’s words marked a clear shift of emphasis for an administration that previously had said it was generally “in charge” but there were limits to what it could do — and that oil giant BP was responsible for stopping the flow and cleaning up the disastrous damage.

“Those who think we were either slow on the response or lacked urgency, don’t know the facts,” Obama said.