WASHINGTON – The Food and Drug Administration uncovered contamination and unsanitary conditions at a British flu vaccine manufacturing plant in 2003 but failed to reinspect it until similar problems caused the loss of half the American vaccine supply in October, the top FDA official said yesterday.

FDA inspectors who visited the Chiron Corporation plant in Liverpool in June 2003 found records of bacteria concentrations a thousand times the expected level, said a report distributed by Democrats at a hearing of the House Government Reform Committee.

The preliminary inspection report from last month indicates in three places that deficiencies found in 2003 had not been corrected.

But Acting FDA Commissioner Lester Crawford said the problems in 2003 and those that tainted this year’s vaccine were unrelated. “The proof of that is that the 2003 vaccine production was completed on schedule and none of it was condemned,” Mr. Crawford said.

Rep. Henry Waxman, a Democrat of California, said Mr. Crawford’s assertion was part of a “pattern of misleading statements.” The FDA might have averted or at least mitigated the vaccine shortage if it had been vigilant, Mr. Waxman said.

Instead, he said, the FDA rejected its inspectors’ recommendations for a formal warning and asked Chiron to correct problems voluntarily.

Even after Chiron indicated on August 25 that several million doses of vaccine had been contaminated, Mr. Waxman said, the agency remained passive, relying on weekly conference calls with the company rather than a new inspection.

“My criticism is that the FDA didn’t do enough to stay on top of this,” he said in one of several tense exchanges with Mr. Crawford.

British health authorities suspended Chiron’s license on October 5, citing manufacturing problems at the Liverpool plant.

The company had been expected to ship roughly 50 million doses of its Fluvirin vaccine to America, about half the nation’s anticipated supply.

So far, federal officials have found a few million additional doses from Aventis Pasteur, the other manufacturer of an injectable vaccine, and MedImmune, which makes a mist that can be inhaled.

The Bush administration is seeking to acquire another 5 million doses from Canada and Europe.

Mr. Crawford, backed by committee Republicans, strongly defended his agency’s actions in inspecting and monitoring conditions at the Chiron plant.

There was no need for FDA inspectors to return to Liverpool after the June 2003 visit because the company “did what we wanted them to do,” producing a sterile supply of flu vaccine, he said.