* BP reiterates commitment to transparency
* Former Sen. Graham to co-chair Obama's oil spill panel
* BP shares fall more than 4 percent in London
By Matthew Bigg
VENICE, La., May 22 (Reuters) - Energy giant BP Plc scrambled to contain a month-old seabed well leak billowing crude oil into the Gulf of Mexico on Saturday as anger mounted among affected residents and political leaders in Washington.
A month after the well blowout and rig explosion that killed 11 workers, sheets of rust-colored heavy oil are starting to clog fragile marshlands on the fringes of the Mississippi Delta, damaging fishing grounds and wildlife.
"To me from the very beginning with BP it was nothing but public relations," said Roger Halphen, a south Louisiana school teacher who has worked both in the oil industry and as a commercial fisherman.
"It's just a disaster. Everybody was sleeping on this and now all of a sudden here it is," he said of oil washing up on the coast.
BP's battered reputation has been reflected in its share price which lost more than 4 percent in London on Friday, extending recent sharp losses.
U.S. lawmakers and scientists have accused BP of trying to conceal what many believe is already the worst U.S. oil spill, eclipsing the 1989 Exxon Valdez accident in Alaska. It represents a potential environmental and economic catastrophe for the U.S. Gulf coast.
The London-based energy giant, facing growing federal government and public frustration and allegations of a coverup, said its engineers were working with U.S. government scientists to determine the size of the leak, even as they fought to control the gushing crude with uncertain solutions.
It also reiterated on Friday that it was making an effort to be transparent about the unfolding situation.
"We are committed to providing the American people with the information they need to understand the environmental impact from the spill and the response steps that have been taken," BP's Chief Executive Tony Hayward said in a statement.
"We share with you a strong commitment to transparency. BP is working hand-in-hand with federal, state and local governments to gather data on the seabed and in the water, and to incorporate those learnings so that we can continually improve the effectiveness of our response efforts," he said.
President Barack Obama's administration has kept up the pressure on BP. Obama is naming former Democratic Senator Bob Graham and former Environmental Protection Agency chief William Reilly to co-chair a bipartisan commission to investigate the of spill, a White House official said on Friday.
CONFUSION ABOUT LEAK
The panel is patterned after past commissions that have probed incidents such as the 1986 explosion of the space shuttle Challenger.
BP's next planned step is a "top kill" -- pumping heavy fluids and then cement into the gushing well to plug it. That operation could start next week, perhaps on Tuesday, BP Chief Operating Officer Doug Suttles said.
Adding to the confusion, BP revised downward on Friday an estimate from Thursday that one of its containment solutions -- a 1-mile (1.6 km)-long siphon tube inserted into the larger of two seabed leaks -- was capturing 5,000 barrels (210,000 gallons/795,000 litres) of oil per day.
A BP spokesman said the amount of crude oil it sucked from the leak fell to 2,200 barrels (92,400 gallons/350,000 litres) a day in the 24-hour period ended at midnight on Thursday.
"The rate fluctuates quite widely on this tool," Suttles told reporters at a briefing in Robert, Louisiana.
Many scientists dismiss an original 5,000 bpd estimate of the total leaking oil -- often defended by BP executives -- as ridiculously low and say it could be as high as 70,000 barrels (2.9 million gallons/11 million litres) per day or more.
"There's a huge amount of uncertainty around that number and it could have a fairly wide range," Suttles said.
A federal panel will release its estimate of the actual flow rate as early as next week, a Coast Guard official said.
Scientists fear parts of the huge fragmented surface slick will be sucked to the Florida Keys and Cuba by ocean currents. (Writing by Ed Stoddard; editing by Mohammad Zargham)