PUBLIC attitudes toward child care have mellowed considerably in the 20 years since President Nixon described day care as a communist plot to destroy the family. The number of children enrolled in child-care centers has quadrupled during the past 15 years. In addition, 9 out of 10 parents responding to a national survey report that they are satisfied with their child-care arrangements.But that may be misleading. Despite the apparent popularity of day care, two recent studies cite evidence of declining quality in group size, child-staff ratios, and staff turnover. One comprehensive survey, sponsored by the National Association for the Education of Young Children and the US Department of Health and Human Services, finds that the average number of children per group in centers has increased 16 percent since the 1970s. Child-staff ratios have risen 25 percent. At the same time, caregivers' real wages have declined by 25 percent to an average of $11,000 a year. High ratios and low wages contribute to high staff turnover. At for-profit chains, the annual staff turnover rate averages 39 percent, according to the study. One of the authors, Sandra Hofferth of the Urban Institute, notes that although parents claim their main concern is quality, "their behavior makes it clear their main concern is cost." A second survey, by researchers at the University of California at Los Angeles, reports substantial declines during the past decade in California's child-care system, long considered a model for its high standards. Their data suggest that lowering the qualifications for staff positions or increasing the number of children per caregiver seriously compromises the quality of care children receive. Many child-care centers across the country offer an enriching home-away-from-home for their young charges. But these reports remind us that others do not. Public acceptance of child care must not be allowed to turn into public apathy about its quality. Assembly lines belong in factories, not day-care centers. When children's well-being is at stake, the price is never right if the care-giving is inadequate.