WASHINGTON  The Bush administration is imposing restrictions on the ability of states to expand eligibility for Medicaid, in an effort to prevent them from offering coverage to families of modest incomes who, the administration argues, may have access to private health insurance.

The restrictions mirror those the administration placed on the State Children’s Health Insurance Program in August after states tried to broaden eligibility for it as well.

Until now, states had generally been free to set their own Medicaid eligibility criteria, and the Bush administration had not openly declared that it would apply the August directive to Medicaid. State officials in Louisiana, Ohio and Oklahoma said they had discovered the administration’s intent in negotiations with the federal government over the last few weeks.

The federal government has leverage over states, because it pays a large share of the costs for Medicaid and the State Children’s Health Insurance Program, and states have to comply with federal standards to get federal money. The insurance program was created for children whose families have too much income to qualify for Medicaid but not enough to buy private insurance.