WASHINGTON -- In a dramatic turn of events, the Obama administration has given BP the go-ahead to remove the containment cap atop the runaway Deepwater Horizon oil well and replace it with a tighter-fitting one in an attempt to stop all the oil now flowing into the Gulf of Mexico, perhaps as soon as the middle of next week.

Also, Interior Secretary Ken Salazar said Friday that the Obama administration plans within a week to issue a new ban on deep-sea oil drilling to replace a moratorium rejected by a federal court.

If BP's procedure starting today is successful, no oil would gush into the Gulf of Mexico for the first time since soon after the Deepwater Horizon exploded in flames on April 20.

Retired Coast Guard Adm. Thad Allen, the Obama administration's point man on the oil spill, said Friday that the current containment cap will be removed today, and installation of the new one will begin three or four days later.

Once the new cap is in place, engineers will attempt to stop oil from flowing out.

"Our first goal," Allen said of the new containment device, "would be to shut the well in. In other words, close all the means of oil to escape."

It was unclear how, after more than 80 days, officials suddenly had a seeming solution to the gushing oil ready in such a short period of time.

Allen didn't say how many days it would be before the cap would be in place, but a timeline that BP provided to Allen on Friday shows that if all things go as planned, BP will be able to close off the well five days after the old containment cap is removed.

If technicians encounter difficulties, that period might stretch to nine days, the timeline showed.

CALM SEAS THE KEY

Bob Dudley, the BP executive in charge of the Gulf oil spill, said in a letter to Allen that included the timeline that switching the containment cap wouldn't begin until hoses are connected that would allow BP to add a third ship to collect oil from the blown-out well.

Allen, however, appeared satisfied that those preparations are well on the way to completion and that engineers "will likely be in a position to be able to start removing the current cap ... tomorrow."

Just Wednesday, Allen had declined to lay odds on whether the Obama administration would approve the new containment cap, and Thursday he remained skeptical that BP would be able to close off the well until mid-August.

Allen laid the decision on the weather, saying forecasters are predicting a seven- to 10-day window of calm.

"We think this weather window presents a significant opportunity for us to accelerate the process of capping -- shutting down the well from the top and increasing the prospects for being able to kill the well from below through the relief wells," Allen said.

Allen also said other events had come together to assuage earlier concerns that capping the well at the top would cause damage to the well itself -- a concern that caused officials to halt the so-called "top kill" effort in late May.

"If there is a problem and we have to release the pressure ... there'll be four different ways to take (crude out) ... and produce it," lessening the pressure.

ROBOTS AT WORK

Allen described a multi-step process of robots unscrewing six bolts to remove the sheared-off riser pipe, strapping together two pipes that will remain so it's easier to fit the containment cap over them, then bolting the new contraption in place and sealing it with a valve.

There are, of course, no guarantees.

For one, while Allen talked of seven to 10 days of calm weather, BP's timeline shows only an eight-day window -- a window just barely long enough to accommodate the work if unbolting the well's riser pipe takes longer than the ideal.

BP also provided Allen with a list of backup plans should the new containment cap take longer to install than anticipated, or not work as officials hope it will.

Among those, Dudley wrote, would be the stationing between the Deepwater Horizon site and the Gulf Coast of nearly 400 boats and more than 50 aircraft that would be expected to spot and scoop up the additional oil that would flow into the Gulf between the time the current containment cap is removed and the time the new one is installed.

PRIMARY BACKUP

The primary backup plan, however, is the completion of connections that would allow oil to flow from the Deepwater Horizon well's failed blowout preventer directly to the Helix Producer I drill ship. Those connections are in place, Allen said, and the Helix producer may begin receiving oil as soon as Sunday.

Having the Helix Producer in place will help ease one immediate negative result of removing the current containment cap -- once it's gone, the 15,000 or so barrels of oil a day that had been collected through it by the Discoverer Enterprise drill ship will spew directly into the Gulf until the new cap is in place.

Allen said, however, that by Tuesday the Helix Producer will be taking on at least as much oil as the Discoverer Enterprise was.

"We're hoping to mitigate the gap without having the capping device on by bringing the Helix producer on board," Allen said.

A NEW DRILLING BAN

During a visit Friday to California, Salazar, the interior secretary, defended the six-month moratorium his agency imposed in May and said the difficulties BP has encountered in containing the massive Gulf spill and dealing with its blown-out well underscore the need for a pause in deep-sea drilling.

"The moratorium we issued on May 28 in my view was right then and is right today. I think it's very legally defensible. I think that the lower court was wrong," Salazar said during a visit to the Santa Monica Mountains National Recreation Area.

"We will move forward and in the coming days announce a new moratorium decision. It will be within the next week," he added.

A federal appeals court Thursday declined to put a hold on an earlier lower court order overturning the ban, while the matter is on appeal.

Salazar said the new moratorium decision will incorporate data gathered in recent weeks.

"All the different work ... we have been overseeing and been involved in has given us new information on the inadequacy of the ability to contain the ongoing spill at the site of the well, the difficulties in having an oil spill response plan that is effective at protecting ecological values," he said.

McClatchy Newspapers and the Los Angeles Times contributed to this story.