Medicaid, one of the fastest-growing government programs for two decades, and the State Children's Health Insurance Program would grow from about 50 million people today to more than 60 million in 2019, according to data from the Congressional Budget Office and Kaiser Family Foundation. That would be the biggest single expansion since Medicaid was created in 1965.

LEGISLATION: Health insurers' support of bill seen waveringPUBLIC HEALTH OPTION: Preferred but not required, White House says

The expansion is designed to cover the poorest adults among the nation's 46.3 million uninsured. It would change a program aimed mostly at children, people with disabilities and elderly nursing home residents into one that includes...