Nearly one-third of the state’s population will be on Medicaid in three years if ObamaCare is upheld by the US Supreme Court, state officials said.

The number of New Yorkers covered by the program could skyrocket by 24 percent, raising the number of those collecting benefits to 6 million from the current 5 million, which includes 3 million in the city.

Medicaid is paid for by federal, state and local governments, and New York’s program costs a total of $53 billion now.

State officials say the reason for the expected surge is clear: the federal Affordable Care Act, which requires citizens to obtain health insurance or face financial penalties.

The law is being challenged in federal court, and the US Supreme Court will determine next year whether it’s constitutional.

Officials project that the mandate — and attached penalties — will prod large numbers of people who qualify for Medicaid but never bothered to sign up, to do so.

The huge increase was mentioned deep in Gov. Cuomo’s 76-page midyear budget report, released last week.

“The number of Medicaid recipients . . . is expected to exceed 6 million at the end of FY [fiscal year] 2015, an increase of 24.4 percent from the FY 2011 caseload of 4.8 million,” the report said.

Even before federal health-care reform, New York’s Medicaid rolls surged — by 700,000 since 2009, or 14 percent — due to the sluggish economy, officials said.

State officials insist the increased Medicaid caseload is manageable because the federal government has agreed to pick up about 90 percent of the costs of new enrollees.

“Our financial plan is able to absorb most of the population growth in Medicaid,’’ said Cuomo budget spokesman Morris Peters.

“The federal government is reimbursing the state for most of the costs. Because of the enhanced reimbursement from the feds, it doesn’t have a financial hit on the state budget.”

Albany’s share is now $21.1 billion, going up to $23.9 billion in three years.

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