WASHINGTON (AP) _ Concerned that Medicaid is not reaching children who need it, President Clinton ordered federal agencies to seek out millions of children who are eligible but not enrolled.

``Nothing can weigh more heavily on your mind than the health of your child,'' Clinton said Wednesday during a visit to Children's National Medical Center. ``I can barely imagine what it would be like to also have to worry about finding the money to pay for your children's health care in the first place.''

Clinton directed eight agencies to make a concerted effort to enroll 3 million uninsured children in Medicaid. The agencies are the Social Security Administration and the departments of Agriculture, Interior, Education, Health and Human Services, Housing and Urban Development, Labor and Treasury.

They run programs that cover many of the children the president is trying to reach, such as WIC nutritional assistance, food stamps, Head Start and public housing. The agencies were instructed to determine which employees come in contact with eligible children, develop a strategy to educate employees and families on Medicaid and state child health programs and identify any laws or regulations that thwart coverage for children.

Extending coverage to Medicaid-eligible children, Clinton said, would go a long way toward insuring 5 million children within five years under the $24 billion Children's Health Insurance Program.

``But if we don't get any new children into the Medicaid program or very few, then we're going to have a very hard time meeting that 5 million goal,'' Clinton said. ``Just the fact that this money has been appropriated is not enough.''

The president was joined by first lady Hillary Rodham Clinton, who said it is particularly imperative to educate poor parents that their children can be covered by Medicaid.

``Unless they come here to the hospital, where someone can help them with financial assistance, they may not even know they are eligible for Medicaid,'' Mrs. Clinton said.

Clinton's fiscal 1999 budget plan includes $900 million over five years for outreach on children's health, including using schools and child care centers to enroll Medicaid-eligible children. States would have the option of automatically enrolling children in Medicaid before completing all of the eligibility and enrollment forms.

Clinton announced that two states, Colorado and South Carolina, have joined Alabama in expanding their state child health coverage under the children's program. Alabama received approval last month to expand coverage to poor children age 14 to 18; Colorado and South Carolina are seeking to provide coverage to all children.

In addition, Clinton said, 14 states have submitted expansion plans to the Department of Health and Human Services, and 30 states are coming up with plans to address coverage for uninsured children.

``I still have a hard time believing that this country, with the finest health care system in the world, cannot figure out how to give affordable, quality health insurance coverage to every single child in America,'' Clinton said. ``This is wrong. If we really want to make America strong for the 21st century, we will correct it.''