Sponsors of bipartisan legislation that would legalize importation of lower-cost prescription drugs are mounting a last-ditch effort to force a Senate vote on the measure this year but face continued resistance from Majority Leader Bill Frist (R-Tenn.).

In a letter written last week and released yesterday, the key sponsors -- three Democrats and three Republicans -- urged Frist to allow a vote this fall despite his recent comments that action was "doubtful" during this session of Congress.

"We understand that there is limited time remaining in this session of Congress, but we believe that American consumers desperately need the relief from high drug costs that our bill will provide," said Minority Leader Thomas A. Daschle (D-S.D.) and Sens. John McCain (R-Ariz.), Olympia J. Snowe (R-Maine), Lincoln D. Chafee (R-R.I.), Byron L. Dorgan (D-N.D.) and Edward M. Kennedy (D-Mass.).

Frist spokeswoman Amy Call replied that she did not believe Frist's position has changed since he said earlier this month that he doubted he could find time to bring up the bill this year. "Safety is the number one concern and until we have a safe way to do it, he's not prepared to bring [the bill] up and send it to the American people," she added.

The bill's backers disagree with Frist's safety argument and contend there is strong public support for the measure, along with as many as 75 votes for it in the 100-member Senate. "Our bill makes safety the top priority while allowing for legal prescription drug importation," the six senators said.

The bill, similar although not identical to legislation the House approved last year, would lift the current ban on purchase of prescription medicines from abroad, where they are often sold at lower cost to consumers because of price controls. Under the Senate bill, drugs made in the United States or manufactured in foreign plants inspected by the U.S. Food and Drug Administration could be re-imported from Canada during the first year after enactment and from many other industrialized countries the following year.

Polls indicate lopsided voter support for drug re-importation, especially among seniors, and many candidates in this fall's elections are using the issue in their campaigns.

Aides to the bill's sponsors said they will continue to try to bring the legislation to a vote before Congress's anticipated recess or adjournment in early October. But they acknowledged they face serious procedural difficulties unless Frist agrees to schedule a vote. Supporters could use a Senate rule allowing a senator or group of senators to call for a vote, but that could be blocked by an objection from opponents.