The Food and Drug Administration may soon approve the first genetically modified animal for human consumption, a highly anticipated decision that is stirring controversy and could mark a turning point in the way American food is produced.

FDA scientists recently gave a boost to the Massachusetts company that wants federal approval to market a genetically engineered salmon, declaring that the altered salmon is safe to eat and does not pose a threat to the environment.

"Food from AquAdvantage Salmon ... is as safe to eat as food from other Atlantic salmon," the FDA staff wrote in a briefing document. Those findings will be presented next Sunday to a panel of scientific experts that will advise top officials at the FDA whether to approve the altered salmon. The panel is holding two days of meetings to hear from FDA staff members, the company behind AquAdvantage and the public.

AquAdvantage is an Atlantic salmon that has been given a gene from the ocean pout, an eel-like fish, which allows the salmon to grow twice as fast as a traditional Atlantic salmon. It also contains a growth hormone from a chinook salmon.

AquaBounty, the Massachusetts company that first applied to the FDA for permission to sell its fish in 1995, said the modified fish is identical to the Atlantic salmon, except for the speed of its growth.

"We've been studying this fish for more than 10 years," said Ronald Stotish, the company's president and chief executive. "In characteristics, physiology, behavior, this is an Atlantic salmon. It looks like an Atlantic salmon. It tastes like an Atlantic salmon."

The team of scientists at the FDA that reviewed AquaBounty's application seems to agree. "We have found no biologically relevant difference between food from [AquaBounty salmon] and conventional Atlantic salmon," the briefing document said.

But independent scientists, consumer groups and environmental organizations are concerned about both the pending decision and the process that the FDA uses to determine whether the genetically modified fish is safe for human health and the environment.

The agency is evaluating the fish as if it were a new veterinary drug, which means that the FDA's deliberations are behind closed doors and that AquaBounty can claim much of the research and other supporting data it supplies to the FDA is confidential.

"Critical information about the whole process has been kept from the public and organizations that focus on these issues," said Wenonah Hauter, executive director of Food and Water Watch, part of a coalition of 31 organizations and restaurant chefs that is demanding that the FDA deny approval of the altered fish. "There's a transparency problem."

Siobhan DeLancey, an FDA spokeswoman, said the agency is following rules. "We do have obligations under the regulations to protect company confidential information," she said.

Hauter and other critics said the information shield makes it difficult for independent scientists to thoroughly analyze claims by AquaBounty or the FDA staff that the altered fish poses no long-term risk to human health or the environment.

Consumer groups and environmental organizations are particularly concerned that AquAdvantage Salmon could escape their fish farms to threaten the wild salmon population, which is severely endangered, Hauter said.

Anne Kapuscinski, a professor at Dartmouth College and an expert on the safety of genetically modified organisms, said she is uncertain how well the FDA is able to assess the risks to the natural world that may be posed by an organism created in a laboratory.

"If you put the top scientific researchers in this area into a room, they would have to work very hard together to figure out the conclusion for ecological risk," Kapuscinski said. "This is very, very complex."

The pending decision is being tracked by biotechnology companies that have invested millions of dollars in developing genetically modified animals for food and are waiting for FDA approval.

Scientists at the University of Guelph in Ontario have asked the FDA to approve their "Enviropig," a hog genetically altered to produce environmentally friendly manure. Hematech of Sioux Falls, S.D., is developing genetically modified cows that are resistant to mad cow disease.

The United States has approved genetically modified plants such as corn and soybean.

The fish decision is expected to reverberate beyond the United States. "If these genetically engineered salmon are approved, it will be setting worldwide precedent because salmon is a global commodity," Kapuscinski said. "It will be the first genetically engineered animal approved for human consumption and for wide-scale farming."

In developing its fish, AquaBounty took an Atlantic salmon and inserted a growth hormone gene from a chinook salmon as well as an "antifreeze" gene from the ocean pout.

Conventional salmon stop growing in cold weather and grow very slowly in the first year of life. But the pout's antifreeze gene allows the salmon to produce growth hormones all year, and the genetically modified fish can grow to market size in 18 months instead of three years, AquaBounty said. That means farmers can speed production and increase yields, the company said.

Stotish said the genetically modified fish can become a sustainable source of food for an exploding global population.