Between 242,000 and 280,000 participants must be removed from the special nutrition program for low-income pregnant women, infants and children (WIC) by September because of rising milk, cheese and fruit prices, state program directors said yesterday.

The Agriculture Department program finances vouchers for special food, such as infant formula, juices and cereals, for about 4.6 million women, infants and children up to age 5 who are determined by public health centers and clinics to be at risk of serious nutritional deficiencies. The $2.1 billion Congress provided for the program in fiscal 1990 is enough to serve half of those who are eligible, according to Dennis H. Bach, president of the National Association of WIC Directors. Bach released a survey on expected cuts yesterday.

But because milk, cheese and fruit prices have risen at two to three times the 4.5 percent rate projected earlier by the Agriculture Department, some states are running short of funds and are beginning to cut their rolls and reduce the amount of special food given to each participant, he said. The Agriculture Department has not requested and Congress has not provided an additional $72 million needed to avoid cuts this year, although the House budget resolution seeks to boost next year's funds by $235 million, Bach said. But the Agriculture Department has reprogrammed about $11 million for WIC in needy states.

"It takes about six months for anemia to show up in lab tests," said Lynn McElroy, director of the Oklahoma program. But before the anemia becomes apparent, she said, children with inadequate nutrition are already beginning to experience less resistance to disease, reduced levels of alertness and other reactions to inadequate diet.

David Paige, a professor of public health at Johns Hopkins University, said the program is designed to ensure that a pregnant woman receives enough nutrients to guarantee normal development of her fetus and that infants get enough to develop their skulls and neurological systems and avert low birth weight, a primary cause of infant mortality.

The survey released by Bach estimated that the WIC rolls in 25 states would have to be cut a total of 242,239 by September. Other states did not face cuts because they were not using funds as quickly. Robert Greenstein, a former director of the Agriculture Department's Food and Nutrition Service and now head of the Center on Budget and Policy Priorities, said a follow-up survey by his group this week found that at least 27 states face caseload reductions totaling nearly 280,000 even after reprogramming the $11 million. An earlier Agriculture Department survey put the expected caseload reduction at 239,223.

A department spokesman said that even if the program drops to 4.4 million by year's end, it still is serving more people than a year ago.