WASHINGTON -- Grilled by skeptical lawmakers, Interior Secretary Ken Salazar on Tuesday acknowledged his agency had been lax in overseeing offshore drilling activities and that may have contributed to the disastrous oil spill in the Gulf of Mexico.

"There will be tremendous lessons to be learned here," Salazar told a Senate panel in his first appearance before Congress since the April 20 blowout and explosion on the Deepwater Horizon rig.

His appearances before two of the three Senate panels holding hearings Tuesday on the giant oil spill came as federal officials kept a wary eye on the expanding dimensions of the problem. The government increased the area of the Gulf where fishing is shut down to 46,000 square miles, or about 19 percent of federal waters. That's up from about 7 percent before.

Government scientists were anxiously surveying the Gulf to determine if the oil had entered a powerful current that could take it to Florida and eventually up the East Coast. Tar balls that washed up on Florida's Key West were shipped to a Coast Guard laboratory in Connecticut to determine if they came from the Gulf spill.

Coast Guard Admiral Thad Allen told the Senate Commerce Committee the growing size and scattershot nature of the oil spill was creating "severe challenges" in containing it and cleaning it up. He called it more complicated than any spill he's ever seen. "What we're basically trying to do is protect the whole coast at one time," Allen said.

New underwater video released by BP PLC, the oil giant that owns a majority interest in the blown well, showed oil and gas erupting under pressure in large, dark clouds from its crippled blowout-preventer device on the ocean floor. The leaks resembled a geyser on land.

Salazar, testifying before the Senate Energy and Natural Resources Committee, promised an overhaul of federal regulations and said blame for the BP spill rests with both industry and the government, particularly his agency's Minerals Management Service. "We need to clean up that house," Salazar said of the service. While most of the agency's 1,700 employees are reliable and trustworthy, he said, there were "a few bad apples."

President Barack Obama, who has decried the "cozy relationship" between government regulators and the energy industry, has proposed splitting the agency into two parts to separate regulatory duties from those who collect royalty fees from oil and gas companies.

Sen. Jeff Bingaman, D-N.M., committee chairman, said the panel's mission was to decipher "the cascade of failures that caused the catastrophic blowout." He said Congress needs to figure what must be done to make sure it never happens again.

Information uncovered so far raises the question of where the Minerals Management Service was, Bingaman said. "It is long past time to drain the safety and environmental swamp that is MMS," declared Sen. Ron Wyden, D-Ore. "This agency has been in denial about safety problems for years."

Sen. John Barrasso, R-Wyo., pointed to an Associated Press investigation that found that rig that exploded was allowed to operate "without safety documentation required by government regulations" and that the government conducted fewer oil rig inspections than it initially claimed and less than its policy requires.

BP said Tuesday it was collecting about 84,000 gallons a day from a mile-long tube drawing oil from the blown-out well to a ship on the surface. It cautioned that increasing the flow through the tube would be difficult.

Obama said he was disappointed that legislation to increase the liability cap for oil spill damages from $75 million to $10 billion had been blocked by GOP objections in the Senate. Objections raised last week by Sen. Lisa Murkowski of Alaska and on Tuesday by Sen. James Inhofe of Oklahoma kept the bill from being passed by bipartisan consent. "This maneuver threatens to leave taxpayers, rather than the oil companies, on the hook," Obama said in a statement.

But BP repeatedly has said it expects to pay out more than the current federal liability cap, and it did so again on Tuesday. "Our intent is to pay all legitimate claims," said Lamar McKay, president of BPAmerica.

"The word 'legitimate' makes me nervous," interrupted Sen. Jay Rockefeller, D-W.Va.

"It shouldn't," McKay said. "It just means it needs to be substantiated."