The Bush administration strongly opposes legislation to give federal health authorities the power to regulate tobacco products, a top official said in a letter to Congress obtained by The Associated Press on Tuesday.

The letter is the strongest indication yet that the administration will try to block the broadly popular legislation, which is supported by majorities in both chambers, and lists both presidential contenders among its co-sponsors. Although a floor vote is expected in the House this summer, a protracted battle with the White House could doom chances for passing the bill this year.

"The administration would strongly oppose this legislation," Health and Human Services Sec. Michael Leavitt said in a July 21 letter to Rep. Joe Barton, R-Texas. Barton is the senior Republican on the Energy and Commerce Committee, which approved the bill on a lopsided 38-12 vote in April. At the time, 11 Republicans on the panel voted in favor of the legislation.

The bill would give the Food and Drug Administration authority to regulate cigarettes and other tobacco products, to reduce the harm from smoking. Although the government would not be able to outlaw tobacco or ban nicotine, regulators could demand elimination of other hazardous ingredients in cigarettes. The bill represents a compromise between anti-tobacco activists and Philip Morris USA, the nation's largest tobacco company.

Leavitt said in the letter that giving a public health agency like the FDA jurisdiction over tobacco products would send the wrong message.

"Unlike the medical products FDA regulates, tobacco products cannot be made safe, and there is no medically established public health benefit associated with tobacco," he wrote. "Adding tobacco to FDA's regulatory responsibilities could also leave the public with the misperception that tobacco products are safe, or at least safer, with the FDA regulating them."

Administration officials had voiced similar concerns before, but had stopped short of declaring outright opposition. Leavitt said in the letter that the White House agreed with his view.

Tobacco control advocates said none of the administration's arguments in the letter were new. "Congress has heard, considered and addressed every one of these criticisms, and key committees in both the House and Senate have voted overwhelmingly and on a bipartisan basis to support the legislation," William V. Corr, executive director of the Campaign for Tobacco-Free Kids said in a statement.

Sens. John McCain, R-Ariz., and Barack Obama, D-Ill., are among the Senate co-sponsors of the bill.