Nearly three-quarters of new mothers in the United States are breast-feeding their babies, but they are quitting too soon and resorting to infant formula too often, federal health officials said Thursday.

A government survey found that only about 30 percent of new moms are feeding their babies breast milk alone three months after birth. At six months, only 11 percent are breast-feeding exclusively.

Formula isn't as good at protecting babies against diseases, eczema and childhood obesity. Ideally, nearly all mothers should breast-feed their babies for six months or more, said Dr. David Paige, a Johns Hopkins University reproductive health expert.

But many do not because of their jobs, the inconvenience, and perhaps because of convincing advertising for baby formula.

What's wrong with giving a baby a bottle every once in a while? Not much, except it can begin a pattern as a child sucks at the breast less, causing less stimulation needed to produce milk, Paige said.

"It creates a downward spiral," he said, adding that often, a woman then moves away from breast-feeding altogether.

The annual random-digit-dial survey by the Centers for Disease Control and Prevention showed that the percentage of women who start breast-feeding rose slightly from 2000 to 2004, from 71 percent to 74 percent. That's a new high, CDC officials said, and is based on nearly 17,000 responses.

A previous survey suggested a higher percentage breast-fed exclusively — 39 percent at three months and 14 percent at six months. However, researchers think there may have been confusion in that earlier survey that led to the higher percentage.

The new results are being called the best national data to date on "exclusive breast-feeding," in which mothers give their infants nothing but breast milk except for vitamin drops.

The CDC study found that rates of exclusive breast-feeding were lowest among black women and among those who are unmarried, poor, rural, younger than 20, and have a high school education or less. Those findings are consistent with earlier studies.

This year, the government announced goals for 2010: getting 60 percent of women to breast-feed exclusively for the first three months and 25 percent through six months.