Last fall, published reports described day-care centers as "major hotbeds" for the spread of hepatitis A, diarrheal diseases and hemophilus influenzae meningitis, a brain disease.

The reports alarmed parents and focused attention on the danger posed by so-called "day-care diseases." But according to most experts, the danger was exaggerated.

"We have enough evidence to make us believe there is an increased risk of disease among children in day care than children in the general population," says Dr. Alfred Bartlett, an epidemiologist who studies day-care disease patterns at the federal Centers for Disease Control in Phoenix, where some of the most serious outbreaks of hepatitis and diarrheal diseases have been reported. "But we don't yet know how much greater that risk is."

Bartlett is the author of the only scientific study to date to compare the incidence of disease among a controlled group of children in and out of day-care centers. In that study, which examined the outbreak of diarrheal diseases over several months among preschool children in the Phoenix area, Bartlett found that children in day care had 1 1/2 times the incidence of diarrheal diseases that children without day care did.

One study in one city, however, does not a final conclusion make, Bartlett stresses. Much more work must be done, he says, before anyone will be able to say precisely how much greater a health risk day-care children face.

Less-serious illnesses, such as coughs, colds, sore throats and chicken pox, of course, long have been the bane of kindergartens and elementary schools.

What day care has done, Bartlett explains, "is move the exposure stage back into early childhood." Most children can manage that, but some cannot.

Dr. Ralph Stiller, a local pediatrician for 29 years, says that while many children attend day care and have no problems, day care can exacerbate the problems of a young child who is prone to coughs, colds, ear infections and the like. That child, especially one younger than 2 and thus unlikely to derive much benefit from group care, may be better off in a family day-care home or with a babysitter.

Outbreaks of diarrheal diseases and hepatitis A are virtually unknown in day-care centers that exclude the so-called diaper trade, according to public health officials. Most of the reported outbreaks of either disease have occurred in cities or regions with large numbers of infant centers, such as the Sunbelt.

In Maryland, there have been no recorded cases of hepatitis or meningitis traced to day-care centers and only one recorded outbreak of diarrheal disease, and that was in a migrant labor camp, according to Dr. Feng-Ying C. Lin, an epidemiologist with the state health department.

In Virginia, the largest outbreak to date was in Richmond in 1981, where 696 cases of diarrheal diseases among parents and children were reported. The disease, health officials say, may have been spread through day-care centers. The only recorded outbreaks of hepatitis A in Virginia occurred in 1968, and those were in elementary schools rather than day-care centers.

In the District, according to Dr. Martin F. Levy, administrator of the city's preventive health services, there have been no reported outbreaks of hepatitis or meningitis, and only a handful of scattered cases of diarrheal diseases.

While warning of the dangers posed by day care, no health officials would suggest that day-care centers be closed. "I'm personally convinced there is a real risk to children of increased disease," Bartlett says. "That doesn't make me think that day care is something that we shouldn't have."

He and others at the CDC say the nation must identify the scope of the problem and find a systematic way of dealing with it. More research and preventive planning, such as a preschool immunization program similar to the one for school-age children, are part of the solution, according to Bartlett.