In a strongly worded letter to Congress, the Food and Drug Administration has come out swinging against proposed legislation that would legalize reimportation of lower-cost pharmaceutical drugs from Canada and other countries.

The letter from Commissioner Mark McClellan to the House Committee on Energy and Commerce said the agency could not guarantee the safety of drugs imported from abroad, and that the bill would "erode" the FDA's ability to oversee the nation's drug supply.

"FDA simply cannot support legislation that exposes Americans to greater potential risk of harm from unsafe or ineffective drugs," concludes the letter, which was delivered to committee chairman W.J. "Billy" Tauzin (R-La.) on Friday.

The letter also estimates that procedures mandated by the bill to reduce the counterfeiting of pharmaceutical drugs would raise the cost of prescription drugs by $2 billion in the first year.

The FDA's position is not a surprise, because the agency has twice before weighed in against legislation to legalize reimportation of cheaper drugs from abroad. But it is taking a more aggressive stance now that the current House bill would effectively take the FDA out of the picture. Objections from the FDA and the Department of Health and Human Services kept the earlier bills from taking effect. Unlike the earlier measures, however, the new legislation does not give HHS authority to block reimportation.

The legislation, introduced by Reps. Gil Gutknecht (R-Minn.) and Jo Ann Emerson (R-Mo.), would make it legal for individuals and pharmacies to import FDA-approved prescription drugs from abroad, where price controls typically keep prices well below those in the United States. Although it is technically illegal, Americans already import sizable quantities of drugs from Canada. McClellan and others have been especially concerned about the safety of drugs being ordered over the Internet.

Efforts to legalize and expand reimportation are hotly opposed by the pharmaceutical industry.

McClellan wrote that the bill would take "unprecedented steps that limit the FDA's authority to assure the safety of prescription drug products." He added that the bill "creates a wide channel for large volumes of unapproved drugs and other products to enter the United States that are potentially injurious to public health and pose a threat to the security of our nation's drug supply."

McClellan said the agency would not be able to ensure the quality of the drugs and would not be able to assure consumers where they were manufactured or whether they had been properly handled.

The agency has recently moved against drug counterfeiters, who it says are increasingly active. Nineteen people were indicted on Monday in Florida for peddling phony or diluted medications.