WASHINGTON - Congressional auditors have found that three-quarters of the nation's immunization programs are rationing one or more childhood vaccines because of shortages. Government officials say supplies are returning to normal.

"Shortages have prompted federal authorities to recommend deferring some vaccinations and have caused the majority of states to reduce or suspend immunization requirements for school and day care programs," said Janet Heinrich, director of health care for the General Accounting Office, the investigative arm of Congress, which wrote the report.

The Centers for Disease Control and Prevention has reported that supplies have returned to normal for most vaccines.

Still, the shortage of vaccine that protects against germs that cause a type of pneumonia, meningitis and ear infections is expected to continue until at least the end of the year, Heinrich said.

"I am particularly concerned that the recent vaccine disruptions will inevitably have a negative impact on vaccine coverage rates in this country," said Sen. Jack Reed, a Rhode Island Democrat. "We are clearly at a point where swift action must be taken to preserve and strengthen our immunization system."

"We simply cannot allow decades of tremendous progress in reducing vaccine-preventable diseases to become undone."

Lawmakers examined the report yesterday at a hearing of a Senate Health, Education, Labor and Pensions subcommittee.

The CDC supports 64 immunization programs - 50 states, eight territories, five cities and the District of Columbia.

Forty-nine of the programs have reported rationing one or more vaccines, the report said.

The nation has experienced shortages of childhood vaccines for the past two years, mainly because some makers dropped out of the market while others slowed production to upgrade manufacturing plants. At one point, the government reported shortages in eight of 11 vaccines.

The report warned that "the potential for recurring shortages will remain."

For instance, investigators noted that only a few companies still produce the vaccines. Five of the eight recommended childhood vaccines have only one manufacturer each.

The report also found that the CDC, required by law to stockpile a six-month supply of recommended childhood vaccines, has stockpiles only for two - one for measles, mumps and rubella and one for polio.