Washington ? Whether Americans opt for Nexium or Prevacid to treat their heartburn, they could have bought the drugs in Canada for less than half the price.

As Congress debates whether to allow foreign pharmacies to fill prescriptions, The Associated Press surveyed comparable U.S. and Canadian prices for 10 popular drugs and found the Canadian prices were 33 percent to 80 percent cheaper.

For example, a three-month supply of cholesterol-controlling Lipitor, the world’s best-selling prescription drug, was 37 percent cheaper in Canada. The anti-depressant Paxil cost about half as much as in the United States, while the arthritis drug Vioxx cost 58 percent less. The biggest price difference was for the anti-psychotic drug Risperdal, 80 percent cheaper in Canada.

“You’re talking about a $40 billion savings, just in what the government dispenses,” said Rep. Jo Ann Emerson, R-Mo., who withheld her support from the House version of a Medicare prescription drug bill until she received assurances from Republican leaders that they would address importation in the final legislation.

Whether to allow Americans to import drugs from Canada and other countries where governments have imposed price controls is among the outstanding issues as lawmakers race to come up with a bill before the end of the year to create a prescription drug benefit for seniors.

Bringing prescription drugs into this country from abroad is now illegal. But the federal government has not tried to block individuals from traveling to Canada to fill their prescriptions.

With Americans facing skyrocketing pharmacy bills, buying drugs in Canada has become a hot political issue, no longer confined to border states where busloads of Americans could make a quick trip north to pick up their prescriptions.

Despite the popular support for allowing imports, the congressional measure is being resisted by politically powerful drug manufacturers as well as the Bush administration and influential lawmakers in both parties, mainly citing safety of Internet sales.