Children receive more medical care if it is offered free, but in general turn out no healthier than children who see doctors less often because their parents are charged for the visit, a new federally funded study has concluded.

The experiment with 1,844 children in six communities suggests that health-care plans requiring some payments by parents will not only cut costs but also keep children as healthy as they would be in more expensive free-care programs, according to Rand Corp. researchers.

"The findings are not going to come as good news to physicians and others who have argued that removing financial barriers to care will result in better health for children," said Robert Valdez, a policy analyst who served as principal author of one report from the Santa Monica-based research group's study.

Some health care experts immediately took issue with the report, funded by the Department of Health and Human Services and based on what Rand called "one of the largest social experiments ever undertaken in this country."

"I have some very severe problems with the study," said Sara Rosenbaum, an attorney who directs the health division of the Children's Defense Fund. "It's very difficult to say what a healthy child is." She said some long-range diseases such as asthma or near-sightedness are detectable only with regular and careful checkups.

Dr. Birt Harvey, a Palo Alto, Calif., pediatrician on the executive board of the American Academy of Pediatrics, said the Rand researchers did not look closely enough at the health of the sampled children to conclude that free-care patients were no better off than what the survey called "cost-sharing" patients.

He noted that the Rand researchers admitted that their conclusions could not be shown to apply to chronically ill or disabled children, since there were not enough of them in the survey for statistical accuracy.

The Rand analysis of the data, collected between 1974 and 1982 in parts of Massachusetts, South Carolina, Ohio and Washington state, appears in two articles in the May issue of the journal Pediatrics.

The researchers assigned volunteer families different health insurance plans at random. Some provided care at no cost, similar to government-funded programs for the poor, and some provided care similar to existing insurance schemes in which families would pay from 25 to 95 percent of their ordinary health costs.

Children on the free-care plan saw a doctor an average 3.5 times a year, compared with three times a year for children whose parents paid some portion of the cost. Free-care children received some kind of medical treatment, not always involving a doctor, 4.4 times a year, compared with only 2.6 annual treatments for children on the 95 percent plan.

The differences showed up only in outpatient care, the study said. The different payment plans did not appear to affect the number of times a child was hospitalized. Also, the cost of each out-patient visit did not vary, an indication that children were getting the same kind of treatment no matter how the bills were paid.

Arleen Leibowitz, a Rand economist who was principal author of the journal paper on utilization of services, said some experts had predicted that parents would short-change preventive care if they had to pay part of their children's medical bills. Although her research does show that preventive care visits declined under cost sharing, parents also reduced the number of visits for acute or chronic illness. So cost-sharing programs reduced both preventive and acute care.

"Insurance companies have typically insured preventive care less generously than care for acute illnes on the grounds that liberal coverage would stimulate excessive use," she said. "Our findings suggest a need to reconsider that rationale."

At the end of the study, the researchers asked parents to rate their children's physical and mental health on a special scale. Then they examined each child for anemia, hay fever, fluid in the middle ear, hearing loss and visual acuity -- each condition selected because it was easy to detect and could have important adverse effects if left untreated.

Valdez and his team qualified their finding that children treated less often on the cost-sharing plan appeared just as healthy as the children on free care. The two groups may have seemed similar in part because the vast majority of American children are usually healthy.

"Only 3 percent of children experienced restrictions in their usual activities; fewer than 10 percent suffered from most chronic problems such as anemia or hay fever," the report said. "Thus, the potential benefit of additional medical care . . . appears limited."

Valdez also noted that only families who could afford paying as much as 50 or even 95 percent of health costs did so. If insurance plans were "not tied to income, cost sharing might have a greater impact than we observed and might adversely affect the health of poor children," he said.

Rosenbaum questioned the need to worry about cutting costs for children's care when the drain on health care dollars was so much greater in care of the elderly and the disabled. Even the Rand study, she noted, identified relatively small differences in annual costs for the various plans. Free care on average cost only $88 a year more per child than 50 percent cost sharing, the study showed.

Both she and Harvey warned against plans that discourage parents from seeking treatment for seemingly small problems.

"A child might sniffle a lot and you'll ignore it," Rosenbaum said. "Only if the child saw a doctor could you discover it was asthma."