KENNER, La. - As BP continued a hydraulic arm-wrestle with its renegade well, President Obama toured Louisiana's soiled beaches Friday and vowed to take personal responsibility for solving the oil spill crisis.

"I am the president and the buck stops with me," he told a televised beach front of Gulf Coast governors, senators, and local officials.

But as demands mount for a more vigorous federal response to the oil seeping into wetlands, curtailing the region's fishing economy, and drying up tourism, Obama also sought to lower expectations.

"America has never experienced an event like this before," he said. "This means that, as we respond to it, not every judgment we make is going to be right the first time out."

Given the magnitude of what he called "a man-made catastrophe that is still evolving," the president added, "There are not going to be silver bullets or a lot of perfect answers for some of the challenges that we face."

Obama's visit, on a humid, nearly windless day, was his second foray to the gulf since the April 20 explosion that killed 11 rig workers and triggered the biggest oil spill in U.S. history. As much as 29 million gallons of oil may have spilled so far, according to government estimates.

Nearly 50 miles offshore, BP struggled to overwhelm the geyser of oil pushing up its well by pumping heavy drilling fluid and other materials into the well at high speed and pressure. BP officials said they had made progress but would be unable to judge the ultimate success of the operation before Sunday.

Chief operating officer Doug Suttles called the operation "a bit like a roller coaster," alternating between shooting in drilling mud, pausing to take pressure tests, and pushing in rubber and other so-called junk materials. "The fact that it stopped and started is not unusual," he said.

Suttles added that engineers were preparing a "riser package" to place over the blowout preventer, and BP is considering stacking another blowout preventer above that apparatus. The drilling of one relief well halted, while another continued.

Obama announced that the federal government would triple the number of personnel involved in the cleanup and monitoring of the spill. So far, 20,000 people have been mobilized, including 1,400 National Guard troops.

Doctors and nurses would be deployed along the coast, paid for by BP, to monitor residents' health and set up a system to track the health effects of the spill, Obama said.

He also pledged that people and businesses affected by the spill could get help by going to the White House website and that the White House would cut through "bureaucratic problems." And in a message seemingly directed at Gulf Coast officials, he said that "if something is not going right," they should contact Coast Guard Adm. Thad Allen or "get in touch with me directly."

"We're on your side and we're going to see this through," Obama said, "until your communities are made whole again. . . . I give the people of this community and the entire gulf my word that we're going to hold ourselves accountable."

While the Louisiana coastline is the only area severely affected, Florida scientists back from a research voyage Friday reported detecting an underwater layer of dissolved hydrocarbons at least 20 miles long beneath the surface of the gulf.

Scientists say the far-flung subsea oil results from the use of dispersants that break up oil on the surface and distribute smaller particles into the water column. "We have all the circumstantial evidence pointing to a layer of oil at 400 meters," said Ernst Peebles, an associate professor of biological oceanography at the University of South Florida.

Peebles said the ship's sonar detected a thick structure at about a quarter-mile deep, about 45 miles northeast of the leaking well. He said scientists found a similar layer of hydrocarbons and particulates at 1,000 meters deep, about 24 miles from the well.

The National Oceanographic and Atmospheric Administration announced Friday that it would launch its own research ship.

NOAA has extended the closed fishing area in the Gulf of Mexico to include a large area of oil-sheen patches crossing the eastern edge of the current boundary, as well as an area currently outside the southern boundary. The closed area represents 60,683 square miles, which is about 25 percent of federal waters in the gulf.

Meanwhile, testifying before a federal investigation panel in Kenner, La., a supervisor on the Deepwater Horizon rig gave a chilling picture of last-minute chaos in the hours before the explosion erupted April 20.

Rig supervisor Christopher Pleasant said he and a colleague had glanced at video monitors and noticed water and mud issuing from the well. Pleasant testified that he tried to contact superiors by ship phone but could not get through. By the time he reached the bridge, there was fire on the deck.

Pleasant said he told the captain, Curt Kuchta, that he wanted to launch the emergency disconnect system, or EDS, designed to detach the rig from the well.

But Kutchta replied, "Calm down. We're not EDS-ing," according to Pleasant. About four to five minutes later, Pleasant said, he launched the procedure anyway, only to find the hydraulic system was not responding.

"I saw that I had no flow, no hydraulics. . . . There were no indications that anything actually happened," he said.

Pleasant said that after he ran to the main deck and saw the fire, "four to five minutes later, the captain said, 'Hit the EDS.' I said, 'I already have.' "

His testimony before a joint panel of the Coast Guard and the federal Minerals Management Service is consistent with other evidence that the rig could not disconnect from the well, which continued to spew oil and gas up a riser pipe to the surface.