Hundreds of vaccination clinics scheduled across the Washington region were canceled abruptly yesterday as public and private health officials struggled to respond to the nation's loss of 48 million doses of influenza vaccine.

In Anne Arundel County, where health officials had expected to administer more than 2,000 shots at their first immunization clinic of the season, nurses from the Department of Health stood in the agency's front driveway handing out notices and waving off people who either hadn't gotten word or had come to make sure they'd heard right.

Private doctors fielded calls nonstop from patients -- or, in pediatricians' offices, from patients' parents. Although they could reassure many patients that, based on age or illness, the vaccine would be available to them, others could only be told to do their best to stay healthy once flu season hits.

"Unfortunately, most feel helpless," said Robert G. Graw Jr., who works with a large family practice in Anne Arundel and Prince George's counties.

The federal government announced Tuesday that nearly half the country's flu shot supply would not be shipped because of possible contamination at a British manufacturing plant in Liverpool. Officials at the Centers for Disease Control and Prevention immediately asked healthy Americans, young and old, to refrain from seeking vaccines so the most vulnerable could be given priority.

Health and Human Services Secretary Tommy G. Thompson said in a conference call that officials had negotiated to get another million doses in addition to the 54 million still expected. Almost half of those have not been distributed, and the director of the CDC said the remaining supply will be directed to areas with the most acute needs.

The CDC cannot require redistribution of supplies already in hand. "We're looking for cooperative ways" of redirecting vaccine to where it is needed most as flu season progresses, said Julie Louise Gerberding, director of the CDC.

One option for those who are not considered vulnerable is a nasal spray. CDC spokesman Ellelwyn Grant said the Gaithersburg producer of the spray, MedImmune, has 1.1 million doses ready for distribution and said it can produce about 1 million more by mid-November.

But that won't help several area agencies that are strapped for enough vaccine even for the high-risk groups.

At the Prince George's County Health Department, a spokesman said the agency has no usable adult doses.

Fairfax County health officials ordered all of their 5,000 adult shots from the Liverpool company, Chiron Corp., and how much they will receive from the remaining manufacturer depends on "how this all shakes out," spokeswoman Kimberly Cordero said.

Loudoun County had anticipated about 9,000 doses from a Chiron distributor and planned to offer nearly a quarter of them for free at Code Flu 04, an emergency drill to test its health agency's ability to provide medication en masse. The Oct. 16 exercise has been postponed.

Karyn Berry, a D.C. senior health deputy, said her agency is evaluating its options. One of the area's largest sources of flu shots acknowledged the same: The Inova hospital system in Northern Virginia was to have received about two-thirds of its nearly 80,000 doses from Chiron. It has a "modest supply" of the alternative vaccine on hand, its Web site notes, and will provide it to high-risk patients at public clinics at its hospitals.

"All other community and workplace flu shot clinics previously scheduled have been canceled," the Web site reports.

The Medstar Health Visiting Nurse Association, which last year vaccinated 18,000 adults across the region, proceeded yesterday with its long-planned appearance at the District law firm of Hogan and Hartson. But nurses emphasized to employees there that the vaccine should be "severely limited" to those in the targeted groups.

With only enough doses on hand to last through mid-October, the association has suspended nearly 300 other dates at private companies and community groups. Clients have been understanding but still want to make sure "to be first in line" if the clinics are resumed, spokeswoman Teresa Cunningham said. "The phone's been ringing off the hook."

Anne Arundel officials are withholding enough of their 4,000 doses to cover residents in nursing homes as well as elderly residents and sick children who cannot get out to be vaccinated. "We will be very, very restrictive in the kinds of settings and populations we supply," said health officer Frances B. Phillips.

She had no prediction of how the public will react to the call for voluntary rationing. Like other health directors and doctors, Phillips worries that the message they have spent several years emphasizing -- that the flu is "not something to be taken lightly" -- will lose potency.

"The irony is that we've been very successful, and now we need to hold back," she said.

People calling Graw's office sounded frightened and confused, he said. "We've told them that they need this, and now there's no vaccine," he said. "They feel it's sort of a betrayal."

Staff writers Bill Brubaker, Michele Clock, Larry Liebert and Paul Schwartzman contributed to this report.

A sign at Riva Road and Truman Parkway reports the cancellation of Anne Arundel's flu shot clinic.Nurse Cathy Carpenter, with Anne Arundel's Health Department, turns away Van and Marilyn Nield of Annapolis.