THE FOOD AND DRUG Administration hasn't always been the highest-profile agency. But concerns over monitoring the safety of drugs after they are on the market, the emerging threat of bioterrorism and the battle about over-the-counter sales of emergency contraceptives underscore the importance of having an FDA that functions effectively and enjoys public trust. That is why, whatever the reason for his sudden departure -- and first indications were that he was asked to leave -- yesterday's announcement that Commissioner Lester M. Crawford is stepping down is such troubling news.

Mr. Crawford was confirmed to the job just two months ago, after serving in an acting capacity for a year and a half and enduring a bruising five-month confirmation process. Overall, the FDA has been without a permanent head for more than half the Bush presidency. This is not a healthy situation for any agency, and certainly not for one whose jurisdiction covers one-quarter of the nation's economy and touches on so many critical issues of public health.

Also unhealthy are the suspicions -- which increasingly appear to have some grounding -- that the supposedly independent agency has been relentlessly politicized. Mr. Crawford, unfortunately, contributed to these perceptions. As a condition of letting his nomination come to a vote, he promised two senators, Hillary Rodham Clinton (D-N.Y.) and Patty Murray (D-Wash.), to make a decision about the emergency contraceptive Plan B -- only to end up deciding that further delay was required. The agency's top official on women's health resigned in protest. "I can no longer serve as staff when scientific and clinical evidence, fully evaluated and recommended for approval by the professional staff here, has been overruled," Assistant Commissioner Susan F. Wood wrote in an e-mail.

We don't yet know the reason for Mr. Crawford's resignation. We do know that President Bush should move quickly to nominate -- and the Senate should, after careful consideration, confirm -- a commissioner with staying power: someone with the scientific expertise, management abilities and strength of character to do one of the most important jobs in government.