Canada has responded with mixed reactions to the shortage of flu vaccine in the United States and to President Bush's suggestion that Canada could fill the gap.

News media have sounded an alarm, warning that hordes of Americans might cross the border to receive flu shots. Clinic officials say they are gearing up for an onslaught, but evidence that it might occur seems to come only from an uptick in telephone inquiries. Canadian border authorities say they've seen no surge of traffic.

Canada's federal officials have seized on the chance to appear magnanimous, with Health Minister Ujjal Dosanjh having said last weekend they would help -- "if there's anything we can spare."

Canada could fill at most about 4 percent of the U.S. shortfall, according to Canadian and U.S. officials. Canada's chief supplier said it might have 1.2 million doses to spare, and Dosanjh's ministry said perhaps another 500,000 to 1 million doses might be excess that could be retrieved from clinics and made available to the United States.

But even that modest contribution is not guaranteed. Canada's vaccines are not approved for use in the United States. The Food and Drug Administration would have to issue an extraordinary immediate approval for the Canadian vaccine, avoiding lengthy clinical trials and regulatory review, U.S. officials said.

At a news conference Tuesday in Washington, the acting commissioner of the Food and Drug Administration, Lester M. Crawford, said the Canadian vaccine might be accepted for use through what is called an "investigational new drug" application. The vaccine would, in effect, be treated as an experimental medicine to be used only for a defined period.

The excess supply of flu vaccine has given Canadians a chance to feel a bit smug about their oft-maligned national health care system.

"Not until everyone in Canada has a flu vaccine. Then you can have some," said Debbie Friesem, 48, a nurse getting her flu shot at Mount Sinai Hospital in Toronto. But wouldn't that be too late for flu season? Her eyes twinkled. "Yes, I guess it would."

Bush focused on Canada as a possible source of flu vaccine when he was asked during last week's presidential debate about the abrupt shortfall in flu vaccine in the United States. The shortage was caused by contamination of the supplies at a plant in Britain owned by the U.S. company Chiron Corp., one of two main suppliers.

Canada's largest vaccine producer, ID Biomedical, had contacted the Food and Drug Administration to say that it could spare 1.2 million doses. But with the U.S. shortfall estimated at 40 million doses, it was a little more than a gesture.

"We knew we could have a limited impact," said Michele Roy, a spokeswoman for the firm, which manufactures the drug in Quebec. She acknowledged that the offer was shrewd; the company is starting a large expansion and had planned to seek FDA approval of its vaccine by 2007.

A spokeswoman for Canada's other supplier, Aventis Pasteur, said it had no extra vaccine. "If they are talking about excess, it's not coming from us," said Nancy Simpson, from the French company's Toronto office.

A report on the national broadcaster CBC talked of a health clinic being "swamped" with calls by Americans and "busloads of Americans turning to Canada in search of flu shots." The National Post newspaper warned of "a growing stream" of "desperate" Americans crossing the border.

The president of the Canadian Medical Association reacted, ordering doctors and clinics to demand proof of residency before administering the needle.

"The stuff that's sitting in my fridge isn't for them," the association's president, Albert Schumacher, said last week. The U.S. problem "is not for us to fix."

The public health administrators in the provinces of Alberta and Ontario put doctors and clinics on notice that the supply of government-provided vaccine was to be used for Canadian residents.

"We're asking for people to provide IDs," said Dan Strasbourg, a spokesman for the Ontario Ministry of Health, which for five years has provided free shots for all residents. "We'd hate for people to make the trip over here and learn they are not eligible for it."

Not all clinics are scrupulous in checking. "All I ask for is a phone number, and I don't look at the area code," said Colleen Silver, 35, a nurse administering the shots in Toronto. But among those waiting in Silver's line for the vaccine, being given in the Mount Sinai Hospital lobby to employees, patients and walk-ins, the opinion was pretty unified: Canadians first.

"I am worried about the Americans coming over," said Susan Shepherd, 46, an accounting manager. "I don't have a problem giving some to them if there's enough here for Canada. But is there enough? I'm very skeptical they are telling the truth."

"We're not getting droves of Americans coming in using our service," said Farah Mohammed, of the charity Victorian Order of Nurses, which runs a clinic in St. Stephen, New Brunswick, on the border with Maine. "But we don't ask for proof of citizenship. We don't turn anyone away who comes to the clinic."

Some Canadians remarked on Bush's sudden embrace of Canadian flu vaccine when his administration has fought to prevent cheaper Canadian drugs from being imported to the United States.

"There is massive hypocrisy on the part of the Bush administration," said Jillian Claire Cohen, an assistant professor of pharmacy at the University of Toronto. "They are very hesitant to allow cheaper, safe drugs from Canada, but when it serves their purposes, all of a sudden they turn to Canada."