The federal official leading the Gulf oil spill cleanup said Friday that a new containment cap and an additional ship collecting oil could effectively contain the spill in the next three days.

The work to replace a leaky containment cap on the well head with a tighter one will begin Saturday, National Incident Commander Thad Allen said Friday. At the same time, a ship connecting to a different part of the leak is expected to come online Sunday.

Allen said he wants BP to take advantage of a current stretch of good weather, "to accelerate the process of capping, shutting in the well from the top and increasing the prospects of killing the well from below through the relief wells."

Oil will flow unimpeded into the Gulf during the cap switch for at least part of the weekend.

Relief wells remain the best chance of stopping the underwater gusher, NPR's Debbie Elliott reports.

"After 80 days, we have to hope they can finally get it right, but they still have to do it," says Ian McDonald, a Florida State University oceanographer. "We've had build up from BP before and they've had failures -- but they've had some successes lately.

If all goes according to plan, the combination of the cap and the new vessel could collect all the leaking oil by Monday. Work continues on what officials hope will be the ultimate solution: a pair of relief wells intercepting the leaking well far below the seafloor.

The new containment cap is expected to form a better seal over the well head, to allow more of the oil to be collected and sent up to ships on the surface for collection or burning.

"Technically it's pretty achievable," Allen said. He said if the new cap can't be placed on the well, the old cap will be put back and there are multiple backup caps available in case any one cap fails.

The new, tighter cap should be in place early Monday. Allen said the ship Helix Producer, which is to be hooked to a different part of the leaking well -- lower than the new cap -- will start collecting oil Sunday and be fully operational Tuesday. He has previously said that the full system should be able to collect 60,000 to 80,000 barrels a day.

The schedule for both efforts has been accelerated to take advantage of what could be a rare window of good weather. The hookup of the Helix Producer was delayed this week by poor weather.

The containment effort is not the permanent solution to stop the environmental catastrophe that began April 20 when the Deepwater Horizon oil rig exploded, killing 11 workers.

Still, the best hope to stop the spewing oil from the blown-out well a mile under the sea is the drilling of relief wells deep below the seafloor. Though officials said the first could be finished by the end of July, weeks ahead of schedule, they are quick to point out that such an optimistic timetable would require ideal conditions every step of the way.

That is something that has rarely happened since the leak began.

"This is a three-act tragedy that we're involved in," says McDonald, the Florida State oceanographer. "Act 1, in which the oil is still spilling out, has gone on forever. Even after it's all plugged, there's still a hell of a lot of oil in the water.

"Act 2 will be the cleanup and the effort to try to undo the environmental damage," McDonald continues. "Act 3 will belong to the lawyers." [Copyright 2010 National Public Radio]