The Bush administration, fighting efforts by states and Congress to expand a popular U.S. health program for children in low-income families, is making it more difficult for families to sign up.

The 10-year-old program was designed to provide medical insurance to children whose families earn too much to qualify for Medicaid, the federal-state program for the poor, and can't afford to buy private health coverage. President George W. Bush has threatened to veto bills passed by the House and Senate to expand funding for Schip, which now covers 6 million children.

The new policy sets more-restrictive standards for states that want to expand eligibility to households above 250 percent of the poverty level, which amounts to $51,625 in annual income for a family of four. Tens of thousands of children would become uninsured in at least 23 states that provide, or plan to provide, coverage exceeding these limits, said Rachel Klein, deputy director of health policy for Families USA, a consumer group in Washington.