One congressman called the nearly six-week oil gush in the Gulf of Mexico an "environmental crime," while a Louisiana senator demanded BP invest $1 billion immediately to protect the region's treasured marshlands.

The failure on Saturday of a "top kill" technique attempted by London-based BP to try to seal its leaking Gulf well has unleashed a surge of anger and frustration that poses a major domestic challenge for President Barack Obama.

Obama, who has called the leaking BP well a "man-made disaster," is trying to fend off criticism that his administration acted too slowly in its response to the spill, now known to be the worst in U.S. history.

He is in a bind because it appears only BP can stop the leak, although he has made clear the government is in charge. But critics say he has not directed enough resources to the unfolding disaster and he has been present enough.

The White House said on Sunday that the government will triple clean-up resources in areas affected by the spill, while the administration's top energy and environment officials head back to the Gulf this week following Obama's second visit on Friday.

"This is probably the biggest environmental disaster we have ever faced in this country," top White House energy adviser Carol Browner told NBC's "Meet the Press."

BP, its reputation and market value already battered by the catastrophic spill, and the entire U.S. oil industry face more probing questions about why safety backups did not accompany their pursuit of oil in ever deeper offshore waters.

"I think without question if the word criminal should be used in terms of an environmental crime against our country, that what's going on in the Gulf of Mexico is going to qualify," U.S. Representative Ed Markey told CBS' "Face the Nation."

Department of Justice officials are part of an ongoing federal investigation into the April 20 rig explosion that triggered the spill, and the Obama administration has not ruled out the possibility of a criminal prosecution.

In Louisiana, which has borne the brunt of the oil spill impact so far, local authorities demanded that BP and the federal government rush a plan to create a sand barrier to the oil by dredging and building up outlying sandbanks and islets.

"I'm devastated ... We are dying a slow death, every time that oil takes out a piece of the marsh, a piece of Louisiana is gone forever," said Billy Nungesser, president of Plaquemines Parish, where the oil has clogged wetlands.

"Even the government seems powerless and all the experts. If these people can't stop it, then who in the name of God can?" Father Gerry, a priest at St. Patrick Catholic Church in Port Sulphur, Louisiana, said, his voice heavy with emotion.