Many scientists say they're skeptical of a widely publicized government report Wednesday that concludes much of the oil that gushed from BP's leaking well is gone and poses little threat to the Gulf of Mexico.

WASHINGTON — Many scientists say they’re skeptical of a widely publicized government report Wednesday that concludes much of the oil that gushed from BP’s leaking well is gone and poses little threat to the Gulf of Mexico.

According to the National Oceanic and Atmospheric Administration (NOAA), the “vast majority” of the 205.8 million gallons released into the Gulf has either evaporated “or been burned, skimmed and recovered from the wellhead, or dispersed.”

BP’s long and halting effort to bring an end to the Gulf of Mexico disaster crossed a key threshold Wednesday when the company packed its ruptured well full of heavy drilling mud, wresting control more than three months after the blowout unleashed one of the world’s largest oil spills.

But officials were not ready to declare dead the renegade offshore well.

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“We have reached a static condition in the well that allows us to have high confidence that there will be no oil leaking into the environment,” retired Coast Guard Adm. Thad Allen, the government’s point man on the spill, said at a White House news briefing. He called it “a very significant step.”

Later Wednesday, Allen gave BP the go-ahead to pump cement into the well through the top. But he continued to emphasize that the battle to permanently seal the well would not be over until one of two relief wells has bored into it sometime in mid-August.

At the White House, officials hailed what they called a “consequential day,” but cautioned it was the end of only one phase in a decades-long recovery effort. After President Obama was briefed on developments, “he thanked me for his birthday present,” joked Carol Browner, Obama’s energy and climate-change assistant. Obama turned 49 Wednesday.

Browner was joined by Allen and Jane Lubchenco, NOAA administrator, at the White House briefing.

An estimated 205.8 million gallons of oil were released by the deep-sea well 50 miles off the Louisiana coast before it was corked with a huge mechanical cap last month.

In trying to figure out where all the oil went, federal scientists concluded that a quarter of it was skimmed, burned or collected and funneled to oil-processing ships. Another 25 percent evaporated or dissolved.

About 24 percent was dispersed into droplets, either naturally or by chemical dispersants that were extensively used to break up the spill.

The rest, 26 percent, is “either on or just below the surface as light sheen and weathered tar balls; has washed ashore or been collected from the shore; or is buried in sand and sediments,” the report concluded.

The White House used the report to boost public confidence that the accident at BP’s drilling site, which killed 11 workers, fouled the Gulf, killed wildlife and disrupted the regional economies from Texas to Florida, is now behind the nation.

Gulf scientists outside the government were skeptical of the analysis.

“I’m suspect if that’s accurate or not,” said Ronald Kendall, the director of the Institute of Environmental and Human Health at Texas Tech University and one of the scientists who testified Wednesday at a congressional hearing about the need for more research into the composition and use of chemical dispersants to break up the oil in the Gulf.

“It’s an estimate, and I’d like to say that even if it’s true, there are still 50 to 60 million gallons that are still out there,” he said. “It’s too early to draw the conclusion that the coast is clear, but there are species there that will tell us.”

Marine conservationist Rick Steiner, a retired University of Alaska scientist, said: “Let’s look at this another way: that there’s some 50 percent of the oil left. It’s still there in the environment.”

The government report also fails to account for the effect of vast, underwater plumes of microscopic droplets of oil that remain unmeasured, scientists said, and it downplays the potential long-term effects of the spill. Some 1.6 billion of gallons were captured at the wellhead.

The remaining 50 percent in the water is the equivalent of almost eight Exxon Valdez oil spills, until now the country’s benchmark environmental disaster.

“Now what we’re hearing is they don’t think the damage will be as bad as they initially thought,” Steiner said. “We have to remember that the same thing was said after the Exxon Valdez. But much of the damage didn’t become apparent until the second or third year.”

Scientists also questioned the report’s methodology.

“There is a lot of uncertainty in these figures,” said James Cowan, Jr., a professor in the Department of Oceanography and Coastal Sciences at Louisiana State University.

For example, the report doesn’t explain how its authors decided what was naturally dispersed oil and what was chemically dispersed oil. They gave no details of how they estimated the evaporation rate of oil — something that’s difficult to do over large areas of seawater, Cowan said.

Lubchenco said the data was “the best direct measurements or estimates that we have at the moment” and that if new information surfaces, the government would adjust its findings “as is always the case in science.”