The spill is threatening an ecological and economic calamity along the US Gulf Coast.

Scientific projections of how much oil has been spewing unchecked for three weeks from the ruptured undersea well has ranged wildly, from BP's 5,000 to 100,000 barrels per day.

BP Chief Operating Officer Doug Suttles appeared on morning US television shows defending the company's efforts to stem the flow and its estimates that about 5,000 barrels of oil were escaping per day.

"I think that's a good range," Suttles said on CNN. "I don't know the precise number, but I think it's somewhere around that number."

On CBS, he added: "We're mounting the biggest response ever done and it's not related to whether it's 5,000 barrels per day or a different number."

BP, Halliburton and Transocean Ltd are all under intense scrutiny over the April 20 Deepwater Horizon rig explosion that killed 11 workers and triggered what could eclipse the 1989 Exxon Valdez spill and become the worst environmental disaster in US history.

Fisheries and tourism, two of the Gulf Coast's economic mainstays, along with birds, sea turtles and other wildlife, are threatened by the spreading slick. The accident also could cripple attempts in Washington to overhaul US energy policy.

BP, whose shares have tumbled and wiped out $30 billion of market value since the rig fire on April 20, has said the oil spill had cost it $450 million so far. BP shares were down about 2 percent in midday trade in London.

The oil slick has broken into smaller parts and as a result may pose less threat of a massive landfall, US Coast Guard Commandant Adm. Thad Allen told reporters on Friday.

But Allen said the spill still "has the potential to be catastrophic, and we need to plan that way."

"The character of the slick has changed somewhat, it is disaggregated into smaller patches of oil," said Allen, who is leading the response to the spill.

Allen said that while dealing with an oil slick broken into different segments is challenging, "that could be to our benefit, because if it does impact shore it's not the whole, it's that portion that came ashore," he said.

BP was moving forward on Friday with its deep sea efforts to stop the unchecked flow of oil.

Suttles told ABC the company hoped to be able to insert a tube into the ruptured riser pipe by late in the day to contain at least part of the leak and siphon oil into a tanker.

"The techniques we're going to try over the next 24 hours, we need to remember, are about trying to contain this leak, they won't stop it," Suttles said.

Other efforts over the next few days include deploying a small containment dome, known as a "top hat," to trap the oil at the site of the leak. If such short-term efforts fail, it could take 90 days for the company to drill a relief well to cap the ruptured one.

The White House has said President Barack Obama  is "deeply frustrated" that the massive mile-deep leak has not been plugged.

Obama and officials in his administration have stressed that BP must pay for the spill's cleanup and other economic impact on the region. The president is expected to repeat that — while putting pressure on the company to achieve results — in a public statement after his meeting on Friday.

Federal authorities said more than 520 vessels are responding to assist in containment and cleanup efforts in addition to dozens of aircraft and undersea remotely operated vehicles working on the ocean floor.

The spill has created complications for Obama's energy policy.

Two lawmakers introduced legislation this week in the US Senate to fight climate change and expand production of renewable fuels, but the spill has dampened the public appetite for an expansion of offshore drilling.