President Barack Obama denounced waste, inefficiency and downright fraud in the government's health care system Wednesday as he sought to rally public support for his revamped overhaul plan.

"Improper payments cost taxpayers almost $100 billion last year alone," Obama said at a rally in this St. Louis suburb.

He said such payments amounted to more than is spent on the Education Department and the Small Business Administration combined, and that if there was a "Department of Improper Payments" it would be "one of the largest agencies in the government."

The president came to Missouri as an installment in presenting a closing argument on his health care overhaul. He says inaction would hurt Americans. It was his second health care speech outside Washington in a week.

Obama cited abuses in the government-run Medicare and Medicaid and in other federal health care programs, citing "payments sent to the wrong person, sent for the wrong reason, sent in the wrong amount."

Sometimes "they're innocent errors" and other times deliberate fraud "by scam artists and fly-by-night" operators, Obama said.

He spoke after Health and Human Services Secretary Kathleen Sebelius, the nation's top health care official, challenged insurers to join Obama's push to overhaul the medical system, arguing that if the effort fails it will hurt them as well as other Americans.