Washington (CNN) -- A "top kill" method intended to stop the runaway flow of oil in the Gulf of Mexico will likely be tried early next week, BP Chief Operating Officer Doug Suttles said Friday.





In the procedure, thick, viscous fluid twice the density of water will be pumped at a high rate into the site of the leak to stop the flow so that it can then be sealed with cement, Suttles said.





"Our best estimate is probably Tuesday," he said, noting that the operation has never been tried in such deep water.





The timing for the "top kill" effort appears to be slipping: BP Managing Director Bo Dudley said Thursday night that the company would try the procedure this weekend.





Suttles offered no explanation for the discrepancy.





"We're working very, very hard with BP on the timeline for the 'top kill,' " said U.S. Coast Guard Adm. Thad Allen, national incident commander. "That's the ultimate near-term solution."





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BP is working to assemble "a massive amount of equipment" at the site, Suttles said, including three deep-water rigs, drilling rigs, sub-sea support vessels and up to 16 robotic submarines.





"These operations are quite complex, and we won't start the job until all the equipment has been staged and all the equipment is in place," he said.





But no one expects the effort to solve all the problems associated with the spill.





"We will not rest, even if they secure the flow, even if this 'top kill' is completed successfully next week," Coast Guard Rear Adm. Mary Landry said. "We have a long row to hoe" to ensure that the damage that has already occurred is mitigated.





Landry expressed disappointment Friday over BP's efforts to clean up oil on the shores of Terrebonne Parish, Louisiana.





Though boom and skimmers had been staged there, "the folks were hesitating in deploying that," she said.





Asked to what degree it will be possible to clean oil from the marshes, Allen said that oil in the marshes is "the worst-case scenario for us to deal with in terms of recovery." That's because mechanical cleanup can do more harm than good, he said.





"In some cases, burning may be an acceptable solution," he said. Any such decision would be made on the scene in consultation with representatives of the state and the parishes involved, he said.





But officials had unqualified praise for the weather, which has been cooperating fully in recent days, leaving the seas dead calm.





"These are ideal conditions for skimming," Landry said, noting that the percentage skimmed has risen to at least 50 percent from the typical 10 percent.





Sub-sea dispersants are also being used, she said, "so we're not seeing a lot of oil coming to the surface."





On Thursday, the Environmental Protection Agency ordered BP to find a less toxic chemical to break up the oil than the one it has been using, Corexit 9500. The chemical has been rated more toxic and less effective than many others on the list of 18 EPA-approved dispersants, according to testimony at a congressional hearing Wednesday.





BP has found no immediate replacement candidate, Suttles said. "Our analysis that we submitted to EPA last night said there were no other dispersants we could identify that were available and less toxic," he said.





BP was to meet later Friday with the EPA to discuss alternatives, he said.





As the continuing spill enters its second month, debate and concern have focused on just how much oil is spewing from the broken riser a mile below the surface. A federal technical team comprising scientists from the federal government and academia has been charged with estimating the flow rate based on video and other data. The estimate will be peer-reviewed and "given rigorous oversight by the federal government and academia," Landry said.





That estimate is likely to be complete "sometime next week,"
What is BP trying to pump fluid for ?
stop the runaway flow of oil in the Gulf of Mexico
question: What is BP trying to pump fluid for ?, answer: stop the runaway flow of oil in the Gulf of Mexico