UPDATE 1-Obama says it's clear "top kill" has not worked

(Adds quotes, background)

* Obama again has strong words over oil spill

* Says all responsible efforts to stop leak will continue

* Faces public opinion battle

By Patricia Zengerle

CHICAGO, May 29 (Reuters) - President Barack Obama said on Saturday that authorities would pursue all "responsible" ways to plug a leaking oil well in the Gulf of Mexico now that it was clear that BP's (BP.L) "top kill" attempt had not worked.

"While we initially received optimistic reports about the (top kill) procedure, it is now clear that it has not worked," Obama said in a statement. "Rear Admiral Mary Landry today directed BP to launch a new procedure whereby the riser pipe will be cut and a containment structure fitted over the leak."

He said the new attempt to stop the flow of oil and gas from the sea floor would be difficult and take several days and that it was not activated until now because it posed risks and had never been attempted before at the depth of the BP spill.

"We will continue to pursue any and all responsible means of stopping this leak until the completion of the two relief wells currently being drilled," said Obama, who has been working to counteract public doubts about his administration's handling of the oil spill.

The relief wells could take several months to complete.

Critics have said the White House has acted neither quickly nor forcefully enough to protect the Gulf waters and coastline and pressure BP to throw all of its resources into trying to stop the flow of oil.

On Friday, Obama interrupted a family vacation in Chicago to make his second trip to the Gulf during the crisis, including a stop at a local beach to inspect protective barriers and witness oil tar balls washed up from the sea.

On Thursday, he held a rare news conference in which he took responsibility for the U.S. response and extended for six months a moratorium on offshore drilling, dealing a potential setback to his own energy policy.

He said his administration would continue to focus on solving the problem.

"As I said yesterday, every day that this leak continues is an assault on the people of the Gulf Coast region, their livelihoods, and the natural bounty that belongs to all of us," he said in the statement.

"It is as enraging as it is heartbreaking, and we will not relent until this leak is contained, until the waters and shores are cleaned up, and until the people unjustly victimized by this manmade disaster are made whole." (Reporting by Patricia Zengerle; Editing by Peter Cooney)