County officials and community groups are putting together a campaign to try to enroll more participants in a program that provides low-cost medical care to uninsured children.

In the past three years, the number of children served by the Medical Care for Children Partnership has fallen 15 percent, to about 6,000. The program's leaders said they are puzzled by the decrease because the number of poor children -- as measured by the number eligible for free or reduced-price school lunches -- has increased.

Administrators said this is the first time in the program's 18-year history that enrollment has fallen.

"This is an unusual year for us," said Andrea Lomrantz, program manager for the Medical Care for Children Partnership.

The program is designed to fill a gap for children whose parents earn too much to qualify for Medicaid or other government health insurance programs but not enough to afford health insurance.

Under the Fairfax program, children in families that earn up to 250 percent of the federal poverty level can get discounted health care -- usually with a $3 co-payment -- from participating doctors and dentists. For a family of four to be eligible, yearly income cannot exceed $48,372.

The declining enrollment has county leaders, school officials and community groups scrambling to find a reason and to figure out how to address it.

They speculate that some low-income families are moving to counties where housing costs are lower.

Enrollment in a similar program in Loudoun County has soared in the past year to 250 children, with 200 on a waiting list, said Carol Jameson, vice president of Northern Virginia Family Service, which administers the Medical Care for Children Partnership. Three years ago there were 100 childen enrolled.

Officials are particularly concerned that Latino families in Fairfax County may be unaware of the program.

"The majority of children in our Fairfax schools who do not have health insurance are Latino children," said Ricardo Cabellos, project coordinator for the county's Office of Partnerships and a member of Gov. Mark R. Warner's Latino advisory commission.

Cabellos said Latinos who are illegal immigrants might be apprehensive about applying for the program. A Virginia law that will go into effect next year will bar illegal immigrants 19 and older from receiving public benefits but will not affect children of illegal immigrants who were born in the United States.

To reach out to uninsured families, school officials have been asked to make sure that new residents get information about the program if they request free or reduced-price lunches. Officials are also pursuing other strategies, including public service announcements in English and Spanish.

They also want to make it easier for families to stay in the program, which requires that parents sign their children up each year.

Among the strategies being explored is making the re-certification process simpler and allowing social workers to write letters on behalf of Spanish-speaking families.

For information on enrolling in the Medical Care for Children Partnerships, call 703-324-5371. Spanish speakers are available.