MIAMI — The Florida manatee, this state’s imperiled environmental icon, last year suffered its most dismal year on record.

Of a population of about 3,200, 416 died in 2006, the highest number of deaths recorded in 30 years of statistics. Many died in collisions with boat propellers.

Now, according to an internal memo, the U.S. Fish and Wildlife Service has been drafting plans under which the celebrated marine mammals would lose their protection as an endangered species.

The planned reclassification of the slow-moving sea cows from “endangered” to “threatened” is expected to elicit a barrage of criticism from environmental groups who see it as a part of the Bush administration’s push to poke holes in the Endangered Species Act.

The new status would make it easier to loosen boating speed limits and restrictions on waterfront development that have been instituted to make Florida safe for the species, environmental leaders said.

“This is absolutely the wrong time to down list manatees,” said Patrick Rose, executive director of the Save the Manatee Club and an aquatic biologist who served as the first federal manatee coordinator. “The terrible thing is, while the last year for manatees was bad, the future could be even worse.”

According to the memo sent from the U.S. Fish and Wildlife Service to the White House, the agency was going to say that the manatee “no longer meets the definition of an endangered species.”

“In Florida, manatees are exhibiting positive growth rates and high adult survival rates along the entire east coast and in the northwest region,” the memo said. “There is still uncertainty about the status of manatees in the southwest region of the state.”

The agency had reached those conclusions after completing a “Five-Year Review” of manatees. But an agency spokesman, while confirming that the recommendation in the memo, dated March 26, reflected the agency’s thinking at the time, said it was possible it might be altered by the time the review is released later this month.

“Until it gets final signatures on it, it could change,” said Chuck Underwood, a spokesman with the agency’s Jacksonville office. “It is an internal document. … Is it the way we’re going at the time? Yes. Is it also possible it could change? Yes.”

He deferred comment about the matter until the review is released.

Environmental groups are already critical of the move.

“We’ve entered the witching hour of the Bush administration where there are going to be frantic lame-duck attempts to do under the table what they cannot pass through Congress,” said Jeff Ruch, executive director PEER, an environmental group which obtained the memo.

The Florida manatees and the legal protections for them have been the subject of a years-long battle pitting environmentalists against some Florida developers and boating groups. While the animals enter other states during the summer, nearly all of them winter in Florida.

By all accounts, the Florida manatee population has increased since the 1970s.

The imposition of boating speed limits or “no wake zones” is believed to have reduced collisions. At the same time, development restrictions helped limit construction in manatee habitats.

But the species continues to face threats from increased boating traffic, red tide outbreaks and waterfront development. The planned closure of some coastal power plants, which have become an artificial refuge for manatees because they release warm water that hundreds of manatees have come to rely on in winter months, is also considered a potentially catastrophic event.

Boating groups and developers have lobbied for weakening some rules meant to protect manatees, arguing that the population is big enough and has become stable.

Developers and boating groups gained a major victory last year, when Florida’s seven-member Fish and Wildlife Conservation Commission approved dropping the endangered label in favor of the threatened label.