Wheezing in babies may foretell asthma.

A sniffling, cold-stricken baby whose breathing sounds like a whistle can send its worried parents racing to the doctor's office. After a few such episodes, however, most parents learn to live with their infants' wheezing. But researchers have wondered whether this wheezing could be an early sign of asthma, a common disorder that leaves its victims gasping for breath.

Now, a new study suggests that while most children outgrow early wheezing, a significant proportion face a high risk of developing asthma. "It's a very important paper in helping us sort out how we can identify [these groups]," says pulmonologist A. Sonia Buist of the Oregon Health Sciences University in Portland. Adds epidemiologist Malcolm Sears of McMaster University in Hamilton, Ontario, "[it] may be possible . . . to reduce the risks of having persistent wheezing and persistent abnormalities in lung function."

The study, headed by epidemiologist Fernando D. Martinez of the University of Arizona College of Medicine in Tucson, tracked 826 children born between 1980 and 1984 and enrolled at birth in a health maintenance organization in Tuscon.

The researchers analyzed data on lung function (measured with lung capacity tests) and allergic sensitivity (measured with blood or skin tests) in the children as infants and at age 6. They also looked at pediatricians' evaluations and questionnaires completed by parents.

Although one-third of the children had had a respiratory tract infection with wheezing before age 3, 60 percent of these children had stopped wheezing by age 6. These "transient early" wheezers had unusually small airways as babies. This could explain why they outgrew their wheezing, says physiologist Wayne J. Morgan, a study coauthor. As their airways grew, they no longer had trouble breathing.

However 113 children, or 13.7 percent of the total, still wheezed at age 6, despite beginning life with normal lung capacity. These "persistent" wheezers showed signs of allergic sensitivity as infants, tended to have mothers with asthma, and had often been diagnosed with the disorder by age 6. The risk of both kinds of wheezing rose in children whose mothers smoked, according to the study, which appears in the Jan. 19 NEW ENGLAND JOURNAL OF MEDICINE.

Asthma strikes over 4 million people under 18, making it the leading chronic illness among children. The number of cases has grown in the past decade for reasons not fully understood.

Sears says the Arizona study imparts a mixed message. "They've given a moderate amount of reassurance in one sense - that early childhood wheezing will tend to go away," he says. "But the less than reassuring thing is this 13 to 14 percent with persistent wheezing, which is an enormous number of children. That fits the fact that we are seeing many, many children with asthma diagnosed throughout childhood."

Morgan cautions that the researchers conducted an epidemiological study, not a clinical trial - they looked at patterns in a population rather than the effects of specific treatments on an illness. So their findings do not imply, for example, that physicians should use drugs such as anti-inflammatory steroids to treat wheezing toddlers of asthmatic mothers.

But the study does point to one way to reduce the risk of wheezing in children, Sears notes: Mothers can avoid smoking, both during and after pregnancy. Parents with an infant at risk of developing asthma can also lower the child's exposure to allergens from cats and household dust, Sears adds.