WASHINGTON — Federal investigators say they have found huge gaps in the regulation of assisted living facilities, a shortfall that they say has potentially jeopardized the care of hundreds of thousands of people served by the booming industry.

The federal government lacks even basic information about the quality of assisted living services provided to low-income people on Medicaid, the Government Accountability Office, a nonpartisan investigative arm of Congress, says in a report to be issued on Sunday.

Billions of dollars in government spending is flowing to the industry even as it operates under a patchwork of vague standards and limited supervision by federal and state authorities. States reported spending more than $10 billion a year in federal and state funds for assisted living services for more than 330,000 Medicaid beneficiaries, an average of more than $30,000 a person, the Government Accountability Office found in a survey of states.

States are supposed to keep track of cases involving the abuse, neglect, exploitation or unexplained death of Medicaid beneficiaries in assisted living facilities. But, the report said, more than half of the states were unable to provide information on the number or nature of such cases.