WASHINGTON — President Obama has declared the swine flu outbreak a national emergency, allowing hospitals and local governments to speedily set up alternate sites and procedures if needed to handle any surge of patients, the White House said on Saturday.

The declaration came when long lines formed around the country for the swine flu vaccine, with distribution that has not met demand.

Flu activity — virtually all of it the swine flu — is now widespread in 46 states, a level that federal officials say equals the peak of a typical winter flu season. Millions of people in the United States have had swine flu, known as H1N1, either in the first wave in the spring or the current wave.

Although no one has an exact count of the flu’s mortality, Dr. Thomas R. Frieden of the Centers for Disease Control and Prevention said Friday that it had killed more than 1,000 Americans and hospitalized over 20,000.

The emergency declaration, which Mr. Obama signed Friday night, has to do only with hospital treatment, not with the vaccine.

A spokesman for the C.D.C., David Daigle, said he had not heard of any hospital that has faced a surge of patients so large that it had to set up a triage area or a treatment unit off-site. He knew of hospitals in Texas and Tennessee that had set up triage tents in their parking lots in order to screen patients with fever or other flu symptoms, but those have been on hospital grounds, he said.

Against this backdrop, administration officials emphasized that Mr. Obama’s declaration was largely a bureaucratic move that did not signify any unanticipated worsening of the outbreak of the H1N1 flu nationwide. Nor, they said, does it have anything to do with the recent reports of vaccine shortages.

“This is not a response to any new developments,” said Reid Cherlin, a White House spokesman. “It’s an important tool in our kit going forward.”

Public and private health officials were administering swine flu shots at scores of locations around the country this weekend.

In Chicago, health officials began giving free vaccinations at six City College locations on Saturday, and within hours officials were turning away hundreds of people because supplies had been exhausted.

Health officials said that they distributed 1,500 doses at each of the sites and that they began the vaccinations at 9 a.m. But two hours before the centers opened, there were already hundreds of people waiting in line for the numbered cards that were needed to get the vaccination. With the number of patients outrunning the supply, officials said that they would give priority to patients who fell into the higher-risk groups.

The seasonal flu typically hospitalizes 200,000 people in the United States each year and kills 36,000. But over 90 percent of the deaths from seasonal flu are among the elderly, while the swine flu mostly affects the young.

The country is in the midst of a serious shortage of swine flu vaccine; only about 16 million doses are available. There is no overall shortage of seasonal flu vaccine — 85 million doses have already shipped, and the regular flu season has not started. But there are temporary local shortages.

The president’s signature on the declaration fulfills the second of two conditions necessary under federal law to empower Kathleen Sebelius, the secretary of Health and Human Services, to issue waivers expediting health care facilities’ ability to transfer patients to other locations. The first condition was met in April when the Department of Health and Human Services declared a public health emergency, which Ms. Sebelius renewed for a second time on Oct. 20.

The declaration allows hospitals to apply to the Department of Health and Human Services for waivers from laws that in normal times are intended to protect patients’ privacy and to ensure that they are not discriminated against based on their source of payment for care, including Medicare, Medicaid and the states’ Children’s Health Insurance Program.

As a practical matter, officials said, the waiver could allow a hospital in danger of being overwhelmed with swine flu patients to remove them, and any emergency room visitors suspected of having the illness, to a location such a local armory to segregate such cases for treatment.

In a few cases, hospitals already have set up tents on their sites. But under federal law, if the patients are sent off-site, the hospital might be refused reimbursement for the care as a sanction.

Since last winter’s more isolated cases of swine flu, the expectation that the virus would return with a vengeance in this flu season had posed a test of the Obama administration’s preparedness. Officials are mindful that the previous administration’s failure to better prepare for and respond to Hurricane Katrina in 2005 left doubts that dogged President George W. Bush to the end of his term.

Jackie Calmes reported from Washington, and Donald G. McNeil Jr. from New York. Crystal Yednak contributed reporting from Chicago.