Rep. Edward Markey, D-Mass., released a letter Saturday that said instead of complying with the EPA restriction, "BP often carpet bombed the ocean with these chemicals and the Coast Guard allowed them to do it."

Before leaving on a boat tour of recovery efforts Sunday off Venice, La., BP chief operating officer Doug Suttles said the company had operated under a protocol agreed on by the Coast Guard and the federal government.

"Furthermore," spokesman Daren Beaudo said earlier, "we've complied with EPA requests regarding dispersants, which are an EPA-approved and recognized tool in fighting oil spills."

The EPA and the Coast Guard ordered BP on May 24, more than a month after the spill began, to cut the use of chemical dispersants by 75 percent.

The Coast Guard approved 74 waivers over a 48-day period after the Environmental Protection Agency order, according to documents reviewed by the investigators. Only in a few cases did the government scale back BP's request.

The EPA said in a statement that the company slashed its use by 72 percent through mid-July, when engineers placed a cap on the leaking well.

"While EPA may not have concurred with every individual waiver granted by the federal on-scene coordinator, the agency believes dispersant use has been an essential tool in mitigating this spill's impact, preventing millions of gallons of oil from doing even more damage to sensitive marshes, wetlands and beaches and the economy of the Gulf coast," the agency said in a statement.

A spokesman for the Coast Guard did not return calls seeking comment.

The chemical dispersant was effective at breaking up the oil into small droplets to be consumed more easily by bacteria, but the long-term effects to aquatic life are unknown. That environmental uncertainty has led to several spats between BP and the government over the use of dispersants on the surface and deep underwater when oil was spewing out of the well.

BP's apparently generous use of dispersants helps explain why so little oil has been spotted on the surface recently, said Larry McKinney, executive director of the Harte Research Institute for Gulf of Mexico Studies at Texas A&M University-Corpus Christi.

Whether the benefits of dispersants outweigh the possible risks is a "debatable point," he said. They've protected the Gulf Coast's fragile wetlands from heavier bands of oil but are capable of killing shrimp and crab eggs and larvae.

"That's a debate with no right answer," he said.

State waters closed by the spill have slowly reopened to fishing, most recently in Florida, where regulators on Saturday reopened a 23-mile stretch of Escambia County shoreline to harvest saltwater fish. The area was closed June 14 and remains closed to the shrimp and crab harvesting pending additional testing. Oysters, clams and mussels were never included in the closure.

In Alabama, the Department of Public Health lifted all swimming advisories for the Gulf of Mexico.

A temporary cap has held the gusher in check for more than two weeks, and engineers were planning to start Tuesday on an effort to help plug the well for good. The procedure, dubbed the static kill, involves pumping mud and possibly cement into the blown-out well through the temporary cap.

If it works, it will take less time to complete a similar procedure using a relief well that is nearly complete. That effort, known as a bottom kill, should be the last step to sealing the well.

Before the static kill can take place, however, debris needs to be cleared from one of the relief wells. The debris fell in the bottom of the relief well when crews had to evacuate the site last week because of Tropical Storm Bonnie.

The attempt to start plugging the well remains on target for Tuesday, Suttles said in Venice.

Companies working to choke off the oil for good are engaged in a billion-dollar blame game. But the workers for BP, Halliburton and Transocean say the companies' adversarial relationship before Congress isn't a distraction at the site of the April 20 rig explosion, where Transocean equipment rented by BP is drilling relief wells that Halliburton will pump cement through to choke the oil well permanently.

"Simply, we are all too professional to allow disagreements between BP and any other organization to affect our behaviors," Ryan Urik, a BP well safety adviser working on the Development Driller II, which is drilling a backup relief well, said in an e-mail last week.

The roles of the three companies in the kill efforts are much the same as they were on the Deepwater Horizon, the exploratory rig that blew up, killing 11 workers. The Justice Department has opened civil and criminal investigations, hundreds of lawsuits have been filed, and congressional investigators are probing the blast and its aftermath.

BP is trying to move forward from the disaster, which sent anywhere from 94 million to 184 million gallons of oil spewing into the Gulf, announcing once the cap was finally in place that its vilified chief executive, Tony Hayward, would be leaving in October.

*Contributing to this report were Associated Press writers Harry R. Weber in Venice, Michael Kunzelman in New Orleans, and H. Josef Hebert and Matthew Daly in Washington.