By ROBERT PEAR 

WASHINGTON — Enrollment in Medicaid is surging as a result of the Affordable Care Act, but the Obama administration and state officials have done little to ensure that new beneficiaries have access to doctors after they get their Medicaid cards, federal investigators say in a new report.

The report, to be issued this week by the inspector general at theDepartment of Health and Human Services, says state standards for access to care vary widely and are rarely enforced. As a result, it says, Medicaid patients often find that they must wait for months or travel long distances to see a doctor.

The inspector general, Daniel R. Levinson, said federal and state officials must do more to protect beneficiaries’ access to care, in view of the program’s rapid growth. Just since October, the administration says, eight million people with low incomes have enrolled. By 2016, the Congressional Budget Office estimates, one in four Americans will be on Medicaid at some time during the year.