Call it a major show of support for the American family. In a move unprecedented in corporate America, 21 large companies are today launching a $100 million initiative to improve child-care, school-age-care, and elder-care projects around the country. As partners in the American Business Collaboration for Quality Dependent Care, the firms will fund more than 1,000 projects in 45 communities over the next six years. These include plans to train day-care providers, establish science-and-technology camps for school-age children, and create a money-management program for senior citizens. ''It is an incredible commitment, an enormous investment,'' says Ellen Galinsky, co-president of the Families and Work Institute in New York. ''What's important is that these businesses, in a time of business turmoil and real competition for dollars, see dependent care as an investment. They're not doing it for charity, they're not doing it because it's the right thing to do. They're doing it because they expect this investment will pay off both in terms of the commitment, effectiveness, and productivity of their current workers and the competence of their future employees.'' This $100 million commitment marks the second phase of the American Business Collaboration, which began in 1992 as a national effort to increase the supply and quality of child- and elder-care programs. The money quadruples a $25 million investment in dependent-care programs when the collaborative was formed. The 21 firms funding the latest programs are Aetna Life & Casualty, Allstate Insurance, American Express, Amoco, AT&T, Bank of America, Chevron, Citibank, Deloitte & Touche, Eastman Kodak, Exxon, GE Capital Services, Hewlett-Packard, IBM, Johnson & Johnson, Mobil, NYNEX, Price Waterhouse, Texaco, Texas Instruments, and Xerox. Some of the most significant national ventures center around what the collaboration calls Championship Model Programs. One innovative model, a school-based voice-messaging system, helps working parents become more involved in their children's education. Using individual voice mailboxes, teachers can leave daily messages for parents about homework and school activities. The system will be piloted in 97 schools in 10 cities this month. Studies show that parental involvement in education is a stronger predictor of a child's success than family income or education level. Another pilot project, to begin this fall, will develop national standards of quality for after-school and summer programs. Currently no accreditation exists for these programs. Middle-school youth programs will be a third focus. Referring to 10-to-14-year-olds, Ms. Galinsky says, ''They don't want to be with little kids in after-school programs anymore, but their parents feel they shouldn't be home alone, watching TV and hanging out.'' The fourth model will create backup child- and elder-care programs for employees whose existing care arrangements break down - when a baby sitter fails to show up, for example, or when schools close for a snow day. According to the Child Care Action Campaign in New York, businesses lose $3 billion a year due to employee absences for child-related reasons. David Boldebuck, a marketing education specialist at Eastman Kodak in Rochester, N.Y., knows firsthand the value of such programs. The father of two preschoolers, he has used Kodak's backup care five times. ''It's nice to know that when something happens, we can call and have someone at the house at 8 the next morning,'' he says. ''You've got a security blanket to fall back on.'' Dependent-care experts also hope the $100 million initiative will produce a trickledown effect. ''I see this as a leadership issue,'' says Bradley Googins, director of the Boston University Center on Work and Family. ''This is a call to arms that all employers need to get involved and need to commit themselves to these issues.'' He adds, ''At a time when government is downsizing, corporations are upsizing their involvement with child-care and elder-care issues. It's in their self-interest if they're going to have employees with family responsibilities become as productive as they can be.'' That self-interest, executives say, serves an important purpose. ''If you're doing this just to help employees, you run the risk that as times get tough, those programs are the first to be modified or eliminated,'' says Susan Moriconi, work-life manager for Hewlett Packard. ''Our top management truly believes this is a business issue and a competitive issue, so continuing support is assured.'' Emphasizing the importance of the collaboration, Patty Siegal, executive director of the California Child Care Resource and Referral Network in San Francisco, says, ''It's clear that public resources alone will not meet the needs, especially the need to improve quality. The amount of work to be done to address the supply and quality of work-family issues is so enormous that we need all the partners and all the friends we can get.''