* Obama to visit Louisiana Gulf coast on Friday
* Hundreds attend memorial service for rig blast victims
* BP shares fall in line with market
* BP may cut live undersea feed of oil leak (Updates with Obama on energy legislation)
By Kristen Hays
HOUSTON, May 25 BP Plc warned on Tuesday that a planned attempt to plug its gushing Gulf of Mexico oil well may be delayed or abandoned, as the energy giant faced mounting pressure from the Obama administration to contain the catastrophic spill.
Equipped with underwater robots, BP (BP.L) engineers plan on Wednesday to inject heavy drilling fluids in the mile- (1.6 km) deep well, a tricky maneuver and its latest bid to halt the flowing oil that has shut down fisheries and soiled coastline.
BP executives have repeatedly stressed the so-called "top-kill" procedure is a complex process that has never been attempted before at such depths, but the Obama administration, under public pressure, is impatient for swift results.
Before BP engineers try to seal the well, scientists will run diagnostic tests "over the next day or so" to make sure the top-kill procedure does not backfire and make the oil leak worse, BP senior vice president Kent Wells told reporters.
Company executives said on Monday the procedure had a 60-70 percent chance of working.
"We have to be careful in terms of setting expectations," said Wells, whose London-based company has seen around 25 percent, almost $50 billion, wiped off its market value.
Shares in BP fell at one point by more than 4 percent on Tuesday, mirroring a fall for European oil and gas stocks .SXEP, before paring losses.
TAKE A LOOK on the spill [ID:nSPILL]
INSIDER TV: link.reuters.com/wuw64k
U.S. Interior Secretary Ken Salazar on Tuesday ordered an investigation of whether his agency failed to properly oversee the oil rig involved in the spill, in light of a new report revealing ethical lapses under prior administrations.
The report found it was common before 2007 for Minerals Management Service employees at a Lake Charles, Louisiana district office to accept gifts from energy company representatives.
After days of lambasting BP's handling of the spill, the Obama administration appeared to step back from Salazar's threat on Sunday to "push out" the company if it did not do enough to plug the leak.
The U.S. government needs BP's deepwater technology to try to shut off the oil well, acknowledged Carol Browner, President Barack Obama's adviser on energy and climate change.
Obama will visit Louisiana on Friday to inspect efforts to combat the spill, the White House said, adding that more than 1,200 vessels and 22,000 personnel had been deployed in "one of the largest responses to a catastrophic event in history."
Analysts say the oil spill could become more of a political liability for Obama ahead of November elections that are widely expected to erode his Democratic party's control of the U.S. Congress.
A CNN/Opinion Research Corporation poll released this week found that 51 percent of Americans were unhappy with Obama's handling of the disaster, despite his administration's efforts to show it is on top of the crisis.
The administration has deflected calls for it to take charge of the operation, saying it is BP's legal responsibility to cap the leak and contain the spreading spill. It stresses that federal authorities have oversight in the operation.
But, state and local officials in affected states like Louisiana have been critical of that approach. Frustrated by BP's failure to seal the well and disperse the oil, they want Obama to take more direct, forceful action.
"He needs to step up to the plate, put somebody in charge that will protect the wetlands and will keep this oil out," said Billy Nungesser, president of Plaquemines Parish, where sheets of heavy oil have already washed into marshlands.
OIL FLOW UNCERTAINTY
Since the April 20 explosion that sank the Deepwater Horizon rig and killed 11 workers, the blown-out well beneath the surface has spewed hundreds of thousands of gallons (liters) of oil into the Gulf in what threatens to become the United States' worst-ever oil spill.
Obama cited the spill when he met Republicans on Capitol Hill on Tuesday and urged them to work with him to pass climate change legislation that aims to reduce U.S. dependence on foreign oil and better protect the environment.
With oil and tar balls from the spill now soiling more than 70 miles (113 km) of Louisiana's 400-mile (644 km) coastline, the U.S. government has declared a "fishery disaster" in the waters off Louisiana, Mississippi and Alabama, making those states eligible for special federal assistance.
Commercial fishing, shrimping and oyster harvests have been shut down for weeks along much of the U.S. Gulf Coast, home to a $6.5 billion seafood industry. Louisiana's industry alone accounts for up to 40 percent of the U.S. seafood supply and more than 27,000 jobs.
BP has estimated that about 5,000 barrels (210,000 gallons/795,000 liters) have been leaking every day, although some scientists have given much higher numbers for the size of the leak -- up to 20 times more.
Besides the "top-kill" option, BP said on Tuesday it was preparing another control method, a lower marine riser package cap containment option, to try to capture and siphon off the oil flowing from the ruptured well. [ID:nLDE64O04Q]
If the short-term efforts fail, it will take BP several months to drill a relief well to stop the leak.
The company said it may shut off a live video link of the oil spewing from a pipe connected to the well when it tries its "top kill" option. "It is under review," a spokesman told Reuters, declining to give a reason for such a move.
Some lawmakers have accused BP of covering up the full extent of the spill, a charge the company has denied.
About 1,000 people attended a memorial service in Jackson, Mississippi for the 11 workers killed in the rig explosion.
The memorial, held in the Jackson Convention Complex, began with the Joyful Gospel Choir singing "This Little Light of Mine." The stage was adorned with a cross and 11 bronzed hard hats, each representing one of the workers who died.
(Additional reporting by Susan Heavey and Matt Spetalnick in Washington, Sarah Young in London; Tom Bergin and Chris Baltimore in Houston, Pascal Fletcher in Miami, Steve Gorman in Los Angeles and Kathleen Baydala in Jackson, Mississippi; Writing by Pascal Fletcher and Ross Colvin; Editing by Paul Simao)