WASHINGTON -- After more than a decade of sharply restricted sales because of health concerns, silicone gel breast implants are poised for an unusual return to the market. The Food and Drug Administration is now reviewing an application to approve the controversial devices, and close observers believe it will rule on the subject later this year.

The National Organization for Women and the consumer group Public Citizen fear the FDA is moving too fast and will call today for the agency to slow its review process considerably. They say that the long-term studies needed to determine whether there is a health risk from silicone gel have not yet been done, and that some scientists remain concerned about serious health consequences.

"We believe that the FDA is rushing to approve silicone gel implants, and we're very concerned about the health consequences for American women," said NOW President Kim Gandy. "Because of the history here, it seems like the FDA is eager to get the issue behind them.

Sidney Wolfe of Public Citizen's Health Research Project, who has highlighted the potential dangers of the silicone implants since 1988, said he believes the FDA will call for an expert advisory panel meeting very soon, and is likely to approve the devices shortly after that.

"In my wildest dreams, I never imagined that 15 years after the dangers of silicone first became known, we would be talking about the implants coming back on the market," he said.

"I think this is a big test for the FDA, and for its new commissioner," said Mark McClellan.

David Feigal, director of the FDA Center for Medical Devices and Radiological Health, said that the agency is reviewing at least one application for silicone gel implants, but it hasn't decided when it will hold a public hearing. He said the issue was among the most emotionally charged that his agency faces, and that it will move carefully.

He said, however, that the complicated relationship between the FDA and the silicone gel industry "inevitably colors how people think about it. There's a long history here."

After concluding that the agency did not have evidence that silicone gel implants were safe, the FDA took them off the market in 1992 except for women who had undergone mastectomies. The decision came after numerous lawsuits claimed that silicone gel implants had caused a range of illnesses.

In 2000, the congressionally funded Institute of Medicine published a review of research on silicone gel implants and concluded that they were not responsible for causing diseases such as breast cancer and connective tissue diseases such as lupus and rheumatoid arthritis. The institute finding was considered something of a rebuke to the FDA.

The report also found that breast implants can cause a host of localized problems and that most will rupture during a woman's lifetime, but many interpreted it as a vote of confidence in silicone gel implants. Soon after, two companies that make the saline implants that replaced them -- and silicone gel implants for sale abroad -- began to press for the FDA to approve silicone gel implants.

One company, Inamed Corp. of Santa Barbara, Calif., applied for FDA approval late last year, and has said it expects a ruling by year's end. Another company that makes implants, Mentor Corp., has also said it intends to seek FDA approval for silicone gel implants.

The debate about FDA approval of silicone gel implants is taking place as breast enlargement has become increasingly popular in the United States. After the silicone gel implants were taken off the market for breast "enhancement," they were replaced by saline implants that have since been approved by the FDA.

About 32,000 women had breast enlargements in 1992, according to the American Society of Plastic Surgeons, but more than 237,000 had them in 2002. (Another 70,000 women got implants after breast surgery.) It is widely believed that if silicone gel implants are approved, the number of women choosing to get breast enlargements will climb even further.

Feigal of the FDA said that the agency is aware that many women believe that silicone gel implants caused them illness and harm. But he also said that the science so far has generally not supported the claim that silicone caused their problems.

What's more, Feigal said, the goal of the FDA is not to approve only those drugs and devices that are entirely safe. The agency, he said, has to weigh the risks and benefits of a product. If the potential benefits outweigh the risks, he said, then "it is reasonable to let consumers decide if they want to take the risks for the potential benefit.

In advance of the calling for an FDA expert panel, NOW organized a scientific meeting in May to discuss silicone gel implants and invited some of the top FDA, National Institutes of Health and academic researchers to address the group. The results of that conference will be released today , and they generally argue that the scientific issues surrounding silicone implants remain open.

Gandy of NOW said the combination of those potential risks for long-term exposure to silicone, plus the fact that most implants will rupture at some point and require additional surgery, make silicone gel implants too risky for American women.

"If the FDA approves silicone gel implants now, women will assume they are safe since they have the FDA seal of approval," she said. They won't think about risks and benefits -- they'll just assume FDA approval of something like this means they're safe. But the science is still inconclusive and the concerns remain."