COVINGTON, La. — Three top Obama administration officials are returning to the Gulf Coast to monitor the massive oil spill that seems to have no end in sight, as BP PLC officials said Sunday that one of their efforts to slow the leak wasn't working as effectively as before. BP spokesman John Curry told The Associated Press on Sunday that a mile-long tube inserted into the leaking well siphoned some 57,120 gallons of oil within the past 24 hours, a sharp drop from the 92,400 gallons of oil a day that the device was sucking up on Friday.