After months of uncertainty and frustration, crews were ramping up efforts to permanently seal the ruptured Gulf of Mexico oil well, which officials said could begin as early today.

The operation is one of two bids to definitively "kill" the damaged well, which has spewed noxious crude into the sea since April, devastating fragile habitats and bringing financial ruin to many residents along the US Gulf Coast.

BP officials in recent days said they hoped the "static kill" operation would take place Tuesday, but on Sunday the US point man for the spill response, Coast Guard admiral Thad Allen, said it "could start as early as Monday night, depending on final testing of the mud injection systems."

If successful, the "static kill" will allow crews to plug the well from above with cement, but the procedure is untested and similar to a previous "kill" attempt that failed at the end of May.

Still, 104 days into the spill, Americans are desperate for a sign that the leak will soon be permanently capped, allowing the full focus of BP and government officials in the region to shift to clean-up operations and repairing the economic damage caused by the worst oil disaster in US history.

Somewhere between three million to 5.3 million barrels leaked into the Gulf between April 20 and July 15, when a cap placed over the wellhead was sealed, fully containing the flow of oil for the first time.

While locals are eager to see the well plugged for good, there are fears that a successful kill operation will prompt a mass exodus of officials brought into the region to respond to the crisis.

Crews have already begun collecting some of the millions of feet of protective boom after skimming vessels said they were having difficulty finding spilled crude on the sea surface anymore.

But the president of Plaquemines Parish in Louisiana told CNN it was too early to scale back those operations.

"The oil is out there," Billy Nungesser insisted, saying that he had ordered his parish sheriff to stop 12 trucks carrying boom from leaving the area.

BP, which leased the Deepwater Horizon rig that exploded April 20, killing 11 workers and sparking the spill, has sought to reassure residents it will remain engaged and work to restore the area.

"There's still a lot to do," BP chief operating officer Doug Suttles told reporters Sunday in Venice, Louisiana.

"There's still oil on the water to pick up. I just stress we're going to be here doing that until the job is completely done," he added.

"I know people are worried about that, will we pack up and go, and the answer is clearly 'No, we're not going to do that.'"

Many fishermen whose grounds were closed in the wake of the spill due to food safety concerns have found work assisting the clean-up effort but face an uncertain future.

They could soon lose their jobs again as there is less oil to mop up and there are no guarantees they will be able to return to fish soon in Gulf waters that could be contaminated for months or even years to come.

But Suttles sought to reassure Americans that Gulf fish and shrimp was safe to eat, telling reporters he "absolutely would" eat Gulf seafood and feed it to his family.

Documents released by Congress Saturday detailing the use of chemical dispersants in the Gulf added to concerns about the long-term effects for the region.

"BP carpet-bombed the ocean with these chemicals, and the Coast Guard allowed them to do it," said Democratic Representative Edward Markey, chairman of the House energy and environment subcommittee.

BP and the US response team have said more than 1.8 million gallons of dispersants have been used to break up the oil, but Markey said studies show the amount could be far higher.

"The validity of those numbers are now in question," he said.

Admiral Allen addressed the concerns Sunday, insisting to reporters that he was "satisfied that dispersants were only used when needed," and that it was the US government on-scene coordinator's decision to use dispersants and not BP's.

Meanwhile on Sunday engineers were carrying out final tests to ensure the integrity of the wellhead, BP said.

Once the static kill is under way, engineers will pump heavy drilling fluid called "mud" into the cap in a bid to push the oil back down into the well reservoir.

If that works, crews will then seal the well from the top with cement.

Then, as early as next weekend, BP plans to begin a "bottom kill" by intercepting the damaged well deep below the seabed with a nearly completed relief well.