In his letter to Food and Drug Administration Commissioner Mark McClellan, Whalen said he felt long-term safety questions remained. Breast implants frequently rupture, and many women believe silicone leaking from the implants can cause serious autoimmune diseases. No major studies have found a connection.

"Long-term safety, the concern that prompted the removal from the market eleven years ago, was clearly not demonstrated, and to approve this device poses threats to women that are clearly unknown," wrote Whalen. He is chief of pediatric surgery at the University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School.

Whalen did not vote at the committee meeting because the chair of device panels only votes in the event of a tie.

His term on the panel had expired in 2002 but he was asked to serve as acting chairman for the October meeting. He said he does not expect to serve on an FDA panel again.

"I regret that the final chapter of my FDA experience was this one and implore you ... not to approve this (application)," Whalen wrote to the FDA.

In an interview Wednesday, Whalen said he felt he had to remain "fair and impartial" at the meeting as chairman. His "increasing discomfort" since the panel meeting prompted him to voice his concerns in the letter, he said.

Copies of Whalen's letter were sent to five members of Congress.

The FDA usually follows recommendations from its advisory panels, which are groups of experts from outside the agency.

FDA spokeswoman Kathleen Quinn said the agency was carefully reviewing Whalen's letter. "It will be part of what we consider," she said.

Inamed, in a written statement, said company officials "remain confident in the FDA's science-based process and their thorough review of the panel's recommendation."

At the panel meeting, Inamed acknowledged its implants carried risks of rupture and repeat operations but said most women in clinical trials were happy with the devices. The company promised long-term monitoring for potential complications, a safeguard panel members said was essential if the implants were approved.

Thomas Gunderson, an analyst for U.S. Bancorp Piper Jaffray, said he felt Whalen's expression of concern would delay the FDA's decision by two to four months but that ultimately Inamed would win approval.

A delay could give rival Mentor Corp. time to "catch up" to Inamed, Gunderson said in a report. Mentor has said it will apply for approval of silicone breast implants by year's end.

Shares of Mentor, also based in California, gained 3 percent to close at $20.60.

Implants filled with saline are widely available, but many women say silicone implants provide a more natural look and feel.