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.

Birnbaum was out after she and her agency came under withering criticism from lawmakers of both parties over lax oversight of drilling and cozy ties with industry.

And after receiving the results of a 30-day safety review from Interior Secretary Ken Salazar, Obama also planned to delay controversial lease sales off the coast of Alaska and cancel entirely plans for drilling lease sales in the Western Gulf and off the coast of Virginia, according to a White House aide.

The officials spoke on condition of anonymity ahead of Obama's midday news conference.