Four underwater vehicles were deployed on Monday under the plan outlined by the coast guard and US Minerals Management Service.
They will dive unmanned to the ocean floor to activate a blowout preventer - a giant series of pipes and valves that could stop the leak.
Swiss-based Transocean Ltd's Deepwater Horizon sank on Thursday, two days after it exploded and caught fire while finishing a well for oil giant BP 68km off the Louisiana coast.
Eleven workers from the rig are missing and presumed dead in what is the worst oil rig disaster in almost a decade. The coast guard on Friday suspended a search forthe workers.
London-based BP, which is financially responsible for the clean-up, has deployed an fleet of ships and aircraft to contain the oil slick.
Tom Atkeson, a coast guard petty officer, told Al Jazeera that workers are doing the best they can to contain the spill.
"We are actively working to both contain and continually skim what is on the surface and stop the flow of oil underneath the water," he said.
"We've sent out 15 response vessels to check on the weather in the area of the oil spill and conduct skimming operations if it is possible at this time."
Atkeson said the environmental damage would be worst if a spill were to reach the Louisiana shore.
"Wind and sea conditions have kept the oil offshore, which is right where we want it, we do not want it to get closer to the shore. We want to be able to deal with it on the open ocean where it's less likely to impact marine life."
Atkeson said the conditions "are changing" and that the US coast guard "are always looking at ways of dealing with the situation if conditions do change".
Weather models predict it will remain about 48km off shore for the next three days.
"We have no shoreline impacts at this time," Rear Admiral Mary Landry, from the US coast guard, said.
The oily sheen covered about 1,036sq km as of Saturday.
'Highly complex task'
Activating the blowout preventer is a "highly complex task" and "it may not be successful," Doug Suttles, the chief operating officer of BP's exploration and production unit, said.
The blowout preventer - which weighs about 450 tonnes and sits on the sea floor next to the well - could take 24-36 hours to activate, he added.
As a back-up, BP is sending two floating drilling rigs to the scene that could drill a series of relief wells to stop the leak. That operation, if needed, could take months, Suttles said.
|The oily sheen covered about 1,036sq km of ocean surface as of Saturday [Reuters]
The explosion came almost three weeks after Barack Obama, the US president, unveiled plans for a limited expansion of US offshore oiland gas drilling.
It has not, however, affected US oil markets.
Transocean said there had been no signs of trouble before the explosion and crews had been doing routine work.
The explosion occurred as the rig was capping a discovery well pending production, company officials said. Some 115 of the 126 workers on board at the time of the explosion were rescued.
The dangers of working on an oil rig have declined in recent decades, but the job remains risky.
Since 2001, there have been 69 offshore deaths, 1,349 injuries and 858 fires and explosions in the Gulf, according to the federal Minerals Management Service.