Washington ? The Senate voted Friday to allow drugs to be imported from Canada, where prices are lower than in the United States, acting for the second time in as many days to hold down the cost of prescription medication.

Even before the 62-28 roll call, the Food and Drug Administration signaled strongly it might use its authority to block the change, warning of a potential security breach and saying it “cannot guarantee the safety of the drugs.”

But that, in turn, drew skepticism from Sen. Byron Dorgan, D-N.D., the chief sponsor of the proposal. He said the Canadian drug supply chain was virtually identical to the one in this country. “It’s virtually impossible … to make a safety issue” out of the proposal, he said.

The Canadian importation provision was added to far-reaching Medicare legislation making its way toward Senate passage next week. That measure would create a new prescription drug benefit for senior citizens, with coverage to be provided by private insurance companies and subsidized by the government.

In addition, it would create a new managed care option for beneficiaries, who would be given the choice of giving up traditional Medicare and enrolling in a preferred provider organization along the lines of plans that now cover millions of working Americans. Overall, the measure would cost $400 billion during the next decade.

Companion legislation is advancing toward a vote in the House next week, and top lawmakers are likely to spend July trying to fashion a compromise. President Bush has made passage of a Medicare bill a priority, saying he wants not only the prescription drug benefit for seniors, but also enough free-market competition to give them more health care choices. At the same time, the White House is seeking changes in Medicare that will solidify finances in advance of a wave of retirements of the baby boom generation.

The vote on drug importation from Canada came one day after the Senate voted to allow generic drug makers to bring their lower-cost medicine to market faster than the current regulatory system allows.

Residents in several states have long made trips to Canada or Mexico to save money on prescription drugs. And while Congress has voted in the past to permit reimportation of drugs from several nations, both the Clinton administration and the Bush administration exercised a provision in the law to block the changes by refusing to certify that the pharmaceutical medicine could be guaranteed safe.

This time, Dorgan limited the proposal to Canadian drugs, a step meant to meet those concerns.

Even so, FDA Commissioner Mark B. McClellan, in a recent letter to Sen. Thad Cochran, R-Miss., wrote that his agency “cannot guarantee the safety of Canadian drugs.” Additionally, he warned against legislation that “creates a wide inlet for counterfeit drugs and other dangerous products that … pose a threat to the security of our nation’s drug supply.”

Dorgan dismissed such claims, citing a report by congressional researchers that the drug supply system in Canada is virtually identical to the one in the United States. He said that under the proposal, licensed pharmacists in the United States would be permitted to purchase drugs from the same supply houses that Canadian pharmacists use.

“A licensed pharmacist in the United States can and should be able to acquire a lower-priced supply of the same drug in Canada and pass those savings along to the consumer,” he said.

Sen. Rick Santorum. R-Pa., said prices are lower in Canada because the government sets them — not an approach the United States should be supporting, he said.

Additionally, Majority Leader Bill Frist, R-Tenn., joined Cochran in citing security concerns over the possibility that Canada could unwittingly be used as a transshipment point for counterfeit drugs by terrorists or others.

While Senate passage of the Medicare bill is expected by a substantial bipartisan margin, Democrats have embarked on a strategy of criticizing the measure, both by proposing changes or by giving speeches that outline their objections.

Sen. Hillary Rodham Clinton, D-N.Y., delivered a lengthy critique of the legislation Friday, saying it “holds tremendous promise and also tremendous peril” for seniors. She backed up her remarks with a chart bristling with circles, boxes and arrows, meant to depict what she said was a “Medicare maze” the legislation would set up.

It was precisely the type of diagram that Republicans used in 1994 to doom the plan for national health insurance that the former first lady hoped to win for her husband, President Clinton.

Sen. Craig Thomas, R-Wyo., said wryly: “The senator from New York represents quite a different point of view than several years past.”

Two Democratic presidential hopefuls also called for changes. Sen. Bob Graham of Florida said he would seek a vote on a plan to close a $1,300 gap in coverage. Sen. John Kerry, D-Mass., said he wanted to use the bill to reduce co-payments for Medicare mental health care to bring them into line with charges for other medical services.

Both men were opposed to the legislation when it cleared the Senate Finance Committee last week, but Kerry said he had not yet made up his mind how to vote on final passage. Clinton also said she had not decided. Graham did not address the subject.