Miami ? For three years, the federal agency in charge of preventing Medicare fraud repeatedly ignored internal watchdog warnings about swindlers stealing millions of dollars by scamming several programs, documents show.

The Centers for Medicare and Medicaid Services received roughly 30 warnings from inspectors over three years during the Bush and Obama administrations but didn’t respond to half of them, even after repeated letters, according to records provided to The Associated Press by U.S. Sen. Charles Grassley’s office.

A July 2008 warning said organized crime had infiltrated the system and was costing more than $1 million dollars for each phony Medicare provider license. The letter got no response, Grassley said. He and other critics said lack of oversight in the federally administered program is part of an estimated $60 billion a year in Medicare fraud.

“There’s no good answer for why the bureaucracy turned a blind eye, and it’s a breach of the public trust,” said Grassley, an Iowa Republican and ranking member of the Senate Finance Committee.

Fighting fraud is key for the Obama administration, which hopes to pay for a large chunk of its proposed national health care overhaul by cracking down on fraud.

Despite the lapses, Obama’s Health and Human Services Secretary Kathleen Sebelius said the Centers for Medicare and Medicaid Services typically responds to fraud warnings promptly, and has investigated more than 300 since 2006. Her office is implementing a new process for tracking the red flags.

Grassley wants the agency to respond to future fraud warnings within two months.

One of the scams involved a program where Medicare patients whose home equipment was damaged or lost in Hurricanes Katrina and Rita get replacements without first getting a doctor’s order. Medical equipment providers were reimbursed for such deliveries, but some of them turned out to be fraudulent.