President Obama denounced Republicans on Tuesday for “playing special-interest politics” after a GOP senator thwarted a Democratic effort to raise the liability cap for oil spills to $10 billion.

Sen. Robert Menendez (D-N.J.) was seeking the unanimous consent of the Senate to move forward on the Big Oil Bailout Prevention Act, which would retroactively boost the legal cap of $75 million on how much companies must pay for economic damages.

But Sen. James M. Inhofe (R-Okla.) blocked the effort, saying it would make drilling too expensive for smaller companies. “Big Oil would love to have these caps there so they can shut out all the independents,” he said, echoing the argument of Sen. Lisa Murkowski (R-Alaska), who halted an identical move last week.

The legislative maneuvering came as federal officials expanded the no-fishing zone to nearly a fifth of the Gulf of Mexico. The closure now totals 45,728 square miles, extending southeast from the blowout site.

BP, the company responsible for the ongoing oil leak in the gulf, released four videos of the underwater well after several days of pressure from members of Congress. A Monday video, aired by Sen. Barbara Boxer (D-Calif.) in the Senate Environment and Public Works Committee, showed a suction tube that BP had inserted to suck up part of the oil from a broken pipe on the sea floor.

“There’s the oil,” Boxer said, noting that it was still spewing despite BP’s efforts. “It’s not doing what a lot of us were hoping it would do.” Boxer’s committee was one of three Senate committees that grilled high-ranking administration officials Tuesday.

Scientists who have suggested that the spill may be several times larger than BP’s estimate of 210,000 gallons a day are scheduled to testify before a House subcommittee Wednesday.

Speaking earlier before the Senate Energy and Natural Resources Committee, Interior Secretary Ken Salazar acknowledged what he called “ethical lapses” on the part of the Minerals Management Service, the agency responsible for overseeing oil drilling on federal land and waters.

“We need to clean up that house,” he said, adding that there were “a few bad apples” among the agency’s 1,700 employees.

BP has pledged to pay all “legitimate” claims of economic damage despite the current cap of $75 million. But Democratic lawmakers want to see a $10-billion cap set into law, just in case BP resists paying what is expected to be billions of dollars in claims.

The April 20 BP blowout is expected to cause billions of dollars in damage to fisheries and tourism, which would be covered by the bill.

The administration has not specified by what amount it wants to raise the cap. But the move to block the liability bill drew a sharp rebuke from Obama.

“This maneuver threatens to leave taxpayers, rather than the oil companies, on the hook for future disasters like the BP oil spill,” he said. “I urge the Senate Republicans to stop playing special-interest politics … and demand accountability from the oil companies.”

Alarm grew in Florida as about 20 tar balls of unknown origin swept up in the Keys. Officials are testing the tar balls to determine whether they came from the spill. The Louisiana Department of Environmental Quality has photographed oil reaching the shore of southern Plaquemines Parish in the Mississippi River Delta.

Jane Lubchenco, head of the National Oceanic and Atmospheric Administration, told the Senate commerce committee that the oil slick could be swept up into the Loop Current, which curls around the Florida Peninsula. But by the time it reaches the Florida Straits, possibly in eight to 12 days, “It would likely be significantly weathered and degraded as well as diluted,” she said.

Simon reported from Washington and Roosevelt from Los Angeles.

richard.simon@latimes.com

margot.roosevelt@latimes.com