Washington ? Kristen Chase plays tennis, lifts weights and works out on cardio machines, an ambitious fitness regimen for a mother of four nearing 40.

But nursing four children has changed the appearance of her breasts in a way exercise can’t fix, she said. So Chase has opted to have surgery to restore her figure, and she has decided silicone gel breast implants would look and feel better than the saline liquid-filled ones.

Her decision would be a simple one in many countries. But in the United States, the Food and Drug Administration bans the use of silicone implants for cosmetic surgery because of lingering suspicions about health risks.

This week, two California companies will go before an FDA advisory panel to seek a recommendation that could open the way to market silicone implants to the 250,000 American women who each year have surgery to make their breasts fuller.

Chase, who lives near Chicago, will be watching closely. She has delayed having the surgery, hoping the panel will ease the ban on silicone implants and the agency will then sign off.

“I don’t want that top-heavy, unnatural look,” she explained. “There are some women that you look at and it’s flagrantly obvious their breasts are augmented.”

Silicone implants have become the choice of 90 percent of European women who have cosmetic breast surgery, according to industry figures. But in this country, they remain limited mainly to cancer patients having breast reconstruction.

In 2003, a FDA panel recommended approval of silicone implants for cosmetic surgery patients, as well. But agency officials rejected that recommendation and requested more information from manufacturers.

The two Santa Barbara, Calif., companies, Inamed and Mentor Corp., have produced data that they say shows a low risk of complications, such as ruptures. But it’s not at all clear the FDA will approve their products.

Even if it approves silicone implants, patients might be required to undergo costly MRI scans every year or two to detect ruptures.

Last week, staff reports released in advance of the panel meeting questioned whether the new industry data reliably can predict that implants would not rupture after more than a few years in women’s bodies.

“The tone of those FDA documents was more negative than people expected,” said Amit Hazan, an analyst who follows the medical devices industry for the investment company of SunTrust Robinson Humphrey.

Wall Street analysts noted that the chairman of the new FDA panel, Johns Hopkins cancer specialist Dr. Michael Choti, voted against silicone implants when he served as a member of the 2003 panel. Choti was not granting interviews, his office said.

For Inamed and Mentor Corp., millions of dollars are riding on the outcome of the three-day meeting.

The safety debate over silicone implants has been going on since the late 1970s. Lawsuits alleging that gel leaking from ruptured implants caused cancer and other diseases forced Dow Corning, a major manufacturer, into bankruptcy. The FDA imposed the current restrictions in 1992.

Since then, repeated scientific investigations have not found a cause-and-effect link between silicone breast implants and illnesses such as cancer, immune system disorders, connective tissue disease or neurological problems.

Supporters of silicone implants conclude that the risks are outweighed by the benefits.

“I’ve never professed that anything man-made in terms of a medical device is perfect,” said Dr. James Wells, a Long Beach, Calif., surgeon who chairs a task force on breast implants for the American Society of Plastic Surgeons.