NEW ORLEANS - A device that's sucking up significant amounts of the oil spewing from the bottom of the Gulf of Mexico offered a measure of optimism yesterday, even as the government's point man on the spill warned problems would persist for months.

Coast Guard Adm. Thad Allen said on CBS' "Face the Nation" that the spill, which is ravaging beaches and wildlife, will not be contained until the leak is fully plugged and that even afterward "there will be oil out there for months to come."

The disaster, which began with an oil rig explosion that killed 11 people in mid-April, will persist "well into the fall," Allen said.

A containment cap placed on the gusher near the sea floor trapped about 441,000 gallons of oil Saturday, BP spokesman Mark Proegler said, up from about 250,000 gallons of oil Friday. It's not clear how much is still escaping; an estimated 500,000 to one million gallons of crude is believed to be leaking daily.

BP chief executive Tony Hayward told the BBC yesterday that he believed the cap was likely to capture "the majority, probably the vast majority" of the oil gushing from the well. The gradual increase in the amount being captured is deliberate, in an effort to prevent water from getting inside and forming a frozen slush that foiled a previous containment attempt.

The next step is for BP engineers to try to close vents on the cap that allow streams of oil to escape and prevent that water intake, and Hayward told the BBC that the company hopes a second containment system will be in place by next weekend. Allen told CBS that the oil would stop flowing only when the leak was plugged with cement.

Hayward, who has faced criticism over his company's response to the spill, told the BBC that he wouldn't step down and that he had the "absolute intention of seeing this through to the end."

"We're going to clean up the oil, we're going to remediate any environmental damage and we are going to return the Gulf coast to the position it was in prior to this event," he said.

Allen took issue on CNN's "State of the Union" yesterday with BP officials who said they were pleased with results of the latest effort. He said progress was being made, "but I don't think anybody should be pleased as long as there is oil in the water."

He said on "Fox News Sunday" that he doesn't "want to create any undue encouragement" and that "we need to underpromise and overdeliver."

BP plans to eventually use an additional set of hoses and pipes to increase the amount of oil being trapped, but the ultimate solution remains a relief well that should be finished by August.