As BP readied its latest fallback plan to stop oil gushing from one of its wells in the Gulf of Mexico, the Obama administration and the company warned that the crude could continue flowing until August, compounding threats to coastal wetlands, fisheries and beaches.

White House energy and climate adviser Carol Browner declared Sunday that the oil spill was “probably the biggest environmental disaster we’ve ever faced in this country” and said that “we are prepared for the worst.” On the CBS show “Face the Nation,” she said that 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.”

Those two wells, which BP began drilling early this month, are expected to intersect the damaged one and seal it near the reservoir far below the seafloor. The first has reached 7,000 feet, and the second has reached a depth of 3,500 feet below the seafloor, but progress gets slower the deeper the wells go. With the arrival of hurricane season Tuesday, the drilling could be slowed if the rigs need to be evacuated during storms.

The grim assessment came in the wake of the failure last week of BP’s “top kill” effort to stop the flow of oil from the damaged well by shooting heavy drilling mud into the hole.

BP Managing Director Bob Dudley, who also made the rounds of Sunday morning shows, said on ABC “This Week” that “the next step is to make sure that we minimize the oil and pollution going into the gulf.” He added: “The main thing now is to contain it.”

BP plans to saw off a bent and broken pipe attached to the five-story tall blowout preventer that sits over the well. The company will then lower a new apparatus that would funnel oil and gas to vessels on the sea surface. But until the new apparatus is in place, cutting the riser pipe will temporarily increase the flow of oil into the sea by 10 percent to 20 percent, the amount that is now being captured by a device that BP inserted farther up the pipe.

Dudley expressed optimism about the latest fallback plan — the fourth so far — saying on CBS, “With this, we think we can contain the majority of the oil and gas.”

The longer oil seeps out of the ground, the more politics are seeping into the public debate as people question why the oil industry and the government were so ill-prepared.

Last week, Gov. Tim Pawlenty, R-Minn., questioned the administration’s reliance on BP’s estimates of the volume of oil, which has been flowing into the gulf since a blowout set fire to the Deepwater Horizon drilling rig, which sank, killing 11 people.

Browner conceded on CBS that “BP has a financial interest in these numbers” on the volume of the leak. “They will pay penalties at the end of the day — a per-barrel, per-day penalty,” she said. But she asserted that the latest, increased estimates of oil flowing from the well were produced by an independent government review panel.

“At the end of the day, the government tells BP what to do, and at the end of the day, we will hold BP accountable for all of this,” she said.

She also sought to portray the administration as in charge and engaged.

Pressed to give an example of administration influence, Browner cited the drilling of two relief wells instead of one. A BP official said that it was “not unusual” to drill a second relief well and that it “very likely” would have been done anyway.

But Browner said that “BP said, ‘We’re going to drill one relief well.’ These are expensive wells for them to drill. We said, ‘That’s not good enough. You’re going to drill a second one.’ ”

BP has said it would take responsibility for damage from the spill, but BP Chief Executive Tony Hayward on Sunday disputed claims by scientists that large undersea plumes have been set adrift by the gulf oil spill.

“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.