The cost over the next five years to fully fund the Special Supplemental Food Program for Women, Infants and Children (WIC) exceeds current estimates by $2.77 billion, a study by the Congressional Budget Office shows.

Prepared for the House Select Committee on Hunger, the study estimated there would be 7.4 million people participating in WIC in 1991 if the program were fully funded. "Nevertheless, we expect . . . 51 percent of eligible women, infants and children will receive WIC benefits," it said.

Raising participation to 85 percent, the study said, would cost $16.96 billion over five years. Eighty-five percent is defined as "full participation," because 15 percent of those eligible for benefits probably will choose not to enter the program, the study said.

The Select Committee on Hunger earlier estimated that full funding could be achieved by fiscal year 1995 by adding $150 million per year to current services, starting from a baseline of $2.126 billion for fiscal 1991. This estimate defined full participation as 80 percent of those eligible.

Under that estimate, the cost for the program, which provides monthly food packages or vouchers to improperly nourished Americans, would be $14.19 billion, which is $2.77 billion (or 19.5 percent) less than the new CBO figures.

"Up to now we never had actual numbers," said committee Chairman Rep. Tony P. Hall (D-Ohio), explaining the wide discrepancy between the estimates. "Now we do. Now we're dealing with reality."

As a rule of thumb, lawmakers believe each WIC participant costs taxpayers $39 per month. The CBO estimated $40.50 per person per month based on analysis of food costs and inflationary trends and their effects on the consumer price index. It would cost $3.6 billion to achieve full funding in one year, the study said.

Hall acknowledged that budget strictures could cripple any attempt to obtain a dramatic increase in the WIC program, but said "there are a lot of people who are committed to full funding."