GULF OF MEXICO - As BP prepared to implement another fallback plan to contain the worst oil spill in U.S. history, Obama administration and BP officials said crude could continue flowing into the Gulf of Mexico until August.

The “American people need to know that it is possible we will have oil leaking from this well until August when the relief wells will be finished,“ presidential energy adviser Carol Browner said on the CBS show “Face the Nation.“

Browner also warned that the spill could get worse for several days as BP attempts to put in place another containment structure. That effort will involve cutting a pipe that rises from the seabed, and because a kink in the riser may be limiting the flow, cutting it could release as much as 20 percent more oil over a period of four to seven days, Browner said.

Hopes for an earlier solution were dashed Saturday when BP conceded defeat in its attempt to plug the well through a maneuver known as a “top kill.“ The effort involved pumping mud into the runaway well, but the pressure of the leak proved overpowering.

The failure of the top kill left a deepening sense of despair in the gulf region, where the spill threatens the ecology, the economy, and a way of life for people in the fishing industry.

Next step: The next step is to try capping the well with a containment structure from which oil can be channeled to the surface and collected.

BP managing director Bob Dudley said on NBC’s “Meet the Press” that the aim of the next maneuver is to contain the majority of the flow. The operation will take four to seven days, and it has a better probability of success than the top kill. The outcome should be clear by the end of this week, Dudley said.

Browner said how much oil the new cap can collect depends on how well it’s fitted over the leak. Other experts also have said installing the new containment valve is risky because of the bend in the riser pipe.

“If they can’t get that valve on, things will get much worse,“ said Philip W. Johnson, an engineering professor at the University of Alabama.

Relief wells: The administration and the oil company say the flow ultimately can be stopped by drilling relief wells, a slow but proven process that is intended to relieve the pressure from the vast undersea oil field. Despite recent setbacks, Browner expressed confidence that the relief wells will work, saying the worst-case scenario is that the spill continues until their expected completion in mid-August.

Oil dispersants: Browner said on CBS’ “Face the Nation” that BP is using oil dispersants on an unprecedented scale, and Environmental Protection Agency Director Lisa Jackson has directed the oil company to “use less.“

“If we have reason to believe that even less should be used, Jackson will issue the appropriate order,“ Browner said.

Criticism of BP: Browner and Rep. Edward J. Markey, D-Mass., chairman of the House energy independence committee, said BP had a financial interest in lowballing its estimate of how much oil is flowing into the gulf. BP initially estimated that roughly 5,000 barrels per day were spewing from the well. However, a group of scientists last week estimated that up to 19,000 barrels are leaking daily.

“If it’s 1,000 barrels per day, it’s a relatively low fine,“ Markey said. “But if it’s 10,000, 15,000 or 20,000 per day, it could wind up billions of dollars in fines that BP executives have to pay.“ He added that BP executives “were either lying, or they were incompetent.“

“If the word ‘criminal’ should be used in terms of an environmental crime against our country,“ Markey said, “what’s going on in the Gulf of Mexico is going to qualify, yes.“

Sen. David Vitter, R-La., said BP “made enormous mistakes and probably cut corners.“ Appearing on CNNs “State of the Union,“ Vitter said the federal government has failed in its response to the crisis, “particularly with the effort to protect our coast and our marsh.“

Cleanup fight: BP’s CEO, Tony Hayward, disputed claims by scientists that large undersea plumes have been set adrift by the gulf oil spill and said the cleanup fight has narrowed to surface slicks rolling into Louisiana’s coastal marshes.

“The oil is on the surface,“ Hayward said. “Oil has a specific gravity that’s about half that of water. It wants to get to the surface because of the difference in specific gravity.“

Scientists from several universities have reported plumes of what appears to be oil suspended in clouds stretching for miles and reaching hundreds of feet beneath the gulf’s surface.

One researcher said yesterday that their findings are bolstered by the fact that scientists from different institutions have come to similar conclusions after separate testing.

“There’s been enough evidence from enough different sources,“ said marine scientist James Cowan of Louisiana State University, who reported finding a plume last week of oil about 50 miles from the spill site that reached to depths of at least 400 feet.