By Chris Baltimore
HOUSTON (Reuters) - BP <:BP.LO:>Plc got government approval to begin a tricky operation to choke off a gushing oil leak in the Gulf of Mexico on Wednesday, and Interior Secretary Ken Salazar said the process was under way.
President Barack Obama said the procedure should greatly reduce or eliminate the flow of crude from the well, but he stressed there was no guarantee it would work.
"We will not rest until this well is shut, the environment is repaired and the cleanup is complete," he said on a trip to California.
BP planned to use undersea robots to inject heavy fluids into the mile- (1.6 km-) deep well and then cement into the seabed well to block oil flow. The so-called "top kill" procedure has never been attempted at such depths.
Asked whether the process had started, Salazar told reporters in Washington: "It's under way." Speaking as he left a congressional hearing into the five-week-old spill, he added: "I am going to watch this happening with the top kill."
The gushing oil leak is an environmental catastrophe that threatens some of the United States' richest fisheries.
The U.S. Coast Guard earlier approved the operation, the most ambitious effort to date to cap the well, after government scientists said it was safe to proceed, according to a statement by the oil spill response command center.
Salazar said he did not know how long it would take BP workers to plug the well. "It depends on what kind of difficulties they encounter as they move forward with the execution" of the plan, he said.
There was no immediate word from BP confirming it had started the operation to block the well. It had said it would decide during the day whether to go ahead with the process, which it said had a 60-70 percent chance of working.
The Coast Guard gave the go-ahead after scientists ran a series of tests to determine whether the procedure had a chance of success or could potentially make the leak worse.
Wednesday is a critical day both for the London-based energy giant and Obama.
BP's reputation and its heavy presence in the United States is at stake, while Obama faces growing criticism from lawmakers and Gulf coast residents over his handling of the spill.
Investors, who have wiped $50 billion off BP's market value since the start of the spill, will watch closely to see whether the procedure works, after a series of earlier attempts failed to plug the leak.
BP shares seesawed in London trading, with hopeful investors boosting the share price about 2.6 percent before closing at 1.4 percent.
The announcement that the U.S. government had approved the operation came after London markets had closed.
If the effort ultimately fails, Obama's government may have no choice but to take central charge of the response to what threatens to become the worst oil spill in U.S. history. It has so far deflected calls for it to take a more direct role and said BP has legal responsibility for fixing the mess.
(Additional reporting by Kristin Hays and Chris Baltimore in Houston, Pascal Fletcher in Miami, Sarah Young in London and Susan Heavey and Tom Doggett in Washington; writing by Ross Colvin; editing by Will Dunham and David Storey)
