WASHINGTON – As the nation prepared for a severe shortage of flu shots, the Food and Drug Administration said yesterday that problems at the British plant that manufactured vaccine withheld by British authorities likely will be used as a “test case” to lobby for better information-sharing with European regulators.

Last Tuesday, British authorities blocked Chiron Corporation from shipping 46 million to 48 million doses of flu vaccine to America. The FDA, which held weekly telephone conversations with Chiron since August 25, said it was stunned by the last-minute about-face.

The agency’s acting commissioner, Lester Crawford, told reporters yesterday that the agency lacked a data-sharing agreement that would have forced its British counterparts to disclose qualms earlier.

British regulators considered the plant’s flu vaccine output “their jurisdiction,” he said, with confidentiality concerns limiting their discussions with the FDA.

“As far as we’re concerned, it’s our regulatory responsibility for those lots that are coming to the United States,” Mr. Crawford said. “I wouldn’t say there is a conflict here, but the two laws do not recognize each other.”

Because the number of companies making vaccines continues to shrink, and many, like Chiron, conduct such manufacturing abroad, they need to be treated like international resources, Mr. Crawford said.

An agency like the World Health Organization could be asked to clarify “the rights and privileges” of the importing country, Mr. Crawford told reporters.

On August 25, Chiron told British and American regulators of bacterial contamination of eight lots of flu vaccine, imperiling up to 8 million doses. Mr. Crawford would not say if the contaminated lots were among vaccine lots the FDA had already cleared for use.

FDA inspectors were in Liverpool when the contamination concerns surfaced, but returned in favor of weekly telephone conferences monitoring Chiron’s progress remedying the problem. Mr. Crawford defended that yesterday as standard operating procedure that worked well in the past.

The agency typically sends two employees to inspect Chiron’s manufacturing plant in Liverpool. After last week’s license suspension, it sent a team of five inspectors.

“There is a crisis,” Mr. Crawford said. The FDA’s fact-finding continues; Mr. Crawford expects a report as early as this week.

Across the nation, flu shot seekers have lined up at clinics for the first wave of 55.4 million vaccine doses produced by Aventis Pasteur for use in America. The Centers for Disease Control and Prevention had hoped to offer 100 million doses of flu vaccine.

As federal authorities continue to struggle to cope with a severe vaccine shortage, one expert said early signs point to a less dangerous flu season than last year.

“My guess is we are going to have a lighter year than last year,” said Dr. Greg Poland, who predicted last year’s staggering flu season.

Dr. Poland, director of the Mayo Clinic’s vaccine research group and one of the government’s vaccine experts, noted that flu outbreaks, thus far, have been small and scattered, the virus hasn’t easily jumped from person to person and it has not triggered early spikes in hospitalizations and deaths.