WASHINGTON (AP) - The head of the troubled agency that oversees offshore drilling resigned under pressure Thursday, Democratic sources said, as President Barack Obama moved more aggressively to take charge of the Gulf oil spill.

The departure of Minerals Management Service Director Elizabeth Birnbaum came just hours before Obama's planned White House press conference on the oil spill, where he was expected to extend a moratorium on new deepwater oil drilling. It was a day of fast-moving developments in Washington and in the Gulf, where engineers worked with some apparent success to stanch the gushing leak five weeks into the catastrophe.