Obama planned to announce that a moratorium on new deepwater oil drilling permits will be continued for six months while a presidential commission investigates the disaster, a White House aide said.

Controversial lease sales off the coast of Alaska will be delayed pending the results of the commission’s investigation, and lease sales planned in the Western Gulf and off the coast of Virginia will be canceled, the aide said, speaking on condition of anonymity ahead of Obama’s news conference.

Those steps, along with new oversight and safety standards also to be announced, are the result of a 30-day safety review of offshore drilling conducted by Salazar at Obama’s direction. Salazar briefed Obama on its conclusions Wednesday night.

The new announcements signaled a fundamental shift in the administration’s policies on offshore drilling, which Obama promoted and hoped to expand prior to the spill. It was just in March that Obama announced a new policy on offshore drilling, throwing open a huge swath of East Coast waters and other protected areas in Alaska and the Gulf of Mexico to drilling. That expansion now looks like it will be dramatically rolled back for some time to come.

Obama will travel to the Gulf Coast on Friday, his second visit since the accident.

The proposed drilling affected by Thursday’s announcements include Shell Oil’s plans to begin exploratory drilling this summer on Arctic leases as far as 140 miles off Alaskan shores. Now those wells will not be considered until 2011.

In Virginia, the lease sales that have been canceled were in an area of about 2.9 million acres 50 miles or more offshore. The sales had already been postponed indefinitely after the spill.

As for the Western Gulf, there was to have been a lease sale in New Orleans in August of 18.8 million acres, located from 9 to about 250 miles offshore. That has been canceled.

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Associated Press Writer Ben Evans contributed to this report.

THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP’s earlier story is below.

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.

THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP’s earlier story is below.

WASHINGTON (AP) — Escalating his administration’s response to the disastrous Gulf oil spill, President Barack Obama plans to announce Thursday that a moratorium on new deepwater oil drilling permits will be continued for six months while a presidential commission investigates, a White House aide said.

Controversial lease sales off the coast of Alaska will be delayed pending the results of the commission’s investigation, and lease sales planned in the Western Gulf and off the coast of Virginia will be canceled, the aide said, speaking on condition of anonymity ahead of a midday Obama news conference.

Those steps, along with new oversight and safety standards also to be announced, are the results of a 30-day safety review of offshore drilling conducted by Interior Secretary Ken Salazar at Obama’s direction. Salazar briefed Obama on its conclusions Wednesday night in the Oval Office.

With the moves, Obama is exerting control over the response to the five-week-old spill amid growing criticism about leadership from the White House, even as BP’s efforts to stanch the leak are finally showing some promise.

The new announcements also could be an early sign of a fundamental shift in the administration’s policies on offshore drilling, which Obama promoted and hoped to expand prior to the April 20 explosion of a drilling rig off the Gulf Coast. The accident killed 11 people and unleashed a sickening gusher of millions of gallons of crude that’s now begun to wash up on land, crippling Louisiana’s fishing and tourism industries along with seabirds and other wildlife.

The exact causes of the accident have not been determined but congressional investigators have released details suggesting BP ignored warning signs of instability in the exploratory well they were attempting to cap when the explosion occurred.

Obama, who last Saturday appointed a presidential commission to conduct a wide-ranging, six-month investigation of the causes of the spill, will travel to the Gulf Coast on Friday, his second visit since the accident.

Thursday’s news conference in the White House East Room represents the first time he’s opening himself to extensive media questioning since the accident occurred.

The proposed drilling affected by Thursday’s announcements include Shell Oil’s plans to begin exploratory drilling this summer on Arctic leases as far as 140 miles off Alaskan shores. Now those wells will not be considered until 2011.

Underscoring the tricky politics of oil drilling, which can cut across party lines, that sparked a protest from Democratic Sen. Mark Begich of Alaska, who issued a press release early Thursday contending Shell could move forward safely and saying “another year of delay costs money and Alaska jobs.”

In Virginia, the lease sales that have been canceled were in an area of about 2.9 million acres 50 miles or more offshore. The sales had already been postponed indefinitely after the spill.

As for the Western Gulf, there was to have been a lease sale in New Orleans in August of 18.8 million acres, located from 9 to about 250 miles offshore. That has been canceled.

It was just in March that Obama announced a new policy on offshore drilling, throwing open a huge swath of East Coast waters and other protected areas in Alaska and the Gulf of Mexico to drilling. That expansion now looks like it will be dramatically rolled back for some time to come.

Under Thursday’s announcement, drilling of new wells in shallow waters is expected to be allowed to continue with additional safety requirements.

For all his power to make such rules, however, when it comes to stopping the spill the president must depend mainly on the company that was leasing the Deepwater Horizon drilling rig when the explosion occurred. BP PLC began a new effort Wednesday to plug the mile-deep well with heavy drilling mud, a tactic never before tried at such depths. The company hoped to know by Thursday afternoon whether the tactic would finally slow the oil spill; as of Wednesday night executives reported no problems so far.

At the Capitol on Thursday, lawmakers will grill various officials at five congressional hearings. Topics will include the Gulf spill’s environmental damage, the administration’s response and the impact on small businesses.

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Associated Press Writer Matthew Daly contributed to this report.