The Agriculture Department deliberately deemphasized and all but suppressed a major research report showing that the special food-supplement program for low-income pregnant women and children substantially improves their health, Rep. George Miller (D-Calif.) said yesterday.

The study says the Women, Infants and Children program significantly cuts premature births and fetal and early-infancy deaths and improves infant birth weight.

John W. Bode, assistant secretary of agriculture for food and consumer services, angrily called Miller's charges "ridiculous."

Study author David Rush, professor of pediatrics and obstetrics at Albert Einstein College of Medicine in New York City, outlined the findings at a news conference convened by Miller and other WIC supporters. The study was based in part on interviews with about 6,000 women.

The program, which began in 1972, provides special vouchers for nutritional foods needed by pregnant women and small children. The program has an appropriation of $1.56 billion for fiscal 1986 and 3.3 million beneficiaries.

Rush said the study showed that women in the program experienced longer pregnancies and fewer premature births than a control group, resulting in 23 percent fewer premature births among whites of low education and 15 percent fewer among similar blacks.

Deaths of the fetus after the 28th week of pregnancy were one-fifth to one-third less frequent among participants.

Miller said the department released the report Jan. 10 when Congress was not in session and omitted the author's summaries, the only parts explaining in plain English the favorable findings of the $6 million, five-year study funded by the department.

Bode said the summaries were deleted because "we did not think in all cases they made a balanced presentation of the findings." But he said the findings showed WIC has a positive effect.