"You wouldn't take risks before your baby's born," the advertisement says. "Why start after?"

Sen. Tom Harkin, D-Iowa, has proposed requiring warning labels, on cans of infant formula and in advertisements, similar to those on cigarettes. They would say that the Department of Health and Human Services has determined that "breast-feeding is the ideal method of feeding and nurturing infants" or that "breast milk is more beneficial to infants than infant formula."

Child-rearing experts have long pointed to the benefits of breast-feeding, but critics say the new campaign has taken things too far and will make mothers who cannot breast-feed, or choose not to, feel guilty and inadequate.

"I desperately wanted to breast-feed," said Karen Petrone, an associate professor of history at University of Kentucky in Lexington.

When her two babies failed to gain weight and her pediatrician insisted that she supplement her breast milk with formula, she said, "I felt so guilty."

"I thought I was doing something wrong," she added. "Nobody ever told me that some women just can't produce enough milk."

Moreover, urging women to breast-feed exclusively is a tall order in a country where more than 60 percent of mothers of very young children work, federal law requires large companies to provide only 12 weeks' unpaid maternity leave and lactation leave is unheard of.

Mothers feel guilty

Only a third of large companies provide a private area where women can express breast milk during the workday, and only 7 percent offer on-site or near-site child care, according to a 2005 national study by the nonprofit Families and Work Institute.

"I'm concerned about the guilt that mothers will feel," said Ellen Galinsky, president of the center. "It's hard enough going back to work."

Public health leaders say the scientific evidence for breast-feeding has grown so overwhelming that it is appropriate to recast their message to make clear that it is risky not to breast-feed.

The goal of a government health initiative called Healthy People 2010 is to get half of all mothers to continue at least some breast-feeding until a baby is 6 months old.

Though about 70 percent of new mothers start breast-feeding right away, just over a third are breast-feeding at 6 months and fewer than 20 percent are exclusively breast-feeding by that time, according to the 2004 National Immunization Survey.