PROJECTIONS OF future trends are not so much guides of what will be as they are warning lights, pointing out problems that need attention and trends that need to be reversed. Forecasters tend to predict that the near future will look a lot like the recent past -- which isn't always true. Twenty years ago, for example, a lot of projections envisioned a more or less permanent continuation of the baby boom. Instead, birthrates plummeted almost to zero-population-growth levels, and so many women got jobs that today 67 percent of women between 16 and 54 are in the labor force.

From today's statistics, the Bureau of Labor Statistics recently projected what the work force will look like in 1995. In some important respects those projections are almost sure to be wrong. For example, will the percentage of women in the work force keep rising? That depends partly on attitudes about which no one can be sure. But the projections, right or wrong, do point out three problems society needs to address.

The first of these is based on hard data. Because of low post-baby-boom birthrates, we know that in 1995 the work force will increasingly consist of people in their prime earning years, age 25 to 54. In the late 1970s and again in the middle 1980s, the American economy has done a splendid job of generating large numbers of low-income, entry- level jobs, providing employment for the baby- boomers, women and immigrants who have made the labor force increase more rapidly in size in the 1970s than in any decade since 1910. The task of the economy in the next 15 years will be different. Now it must start generating larger numbers of higher-skill, prime earning jobs.

A second trend projected by the BLS is less certain and more worrisome. For some years now, lower and lower proportions of young black men have been part of the work force. The projection is that work force participation by black men 16 to 24 will fall from today's 62 percent to 53 percent in 1995, only slightly higher than the 51 percent projected for young black women, and far below the 77 percent for young white men. The implications of the projection for young black men are chilling -- chilling enough, we note hopefully, to inspire the hope from all parts of society that they turn out to be wrong.

The third instructive trend is the lower percentage of people 55 and over in the work force. Often this is benign: one of the things on which an affluent society should spend money is providing retirement and disability income for those no longer readily able to work. The questions remain open, however, whether too many people are going to retire too soon in a society with a rapidly growing number of elderly people, and whether society needs to do something to encourage people who can do so to remain economically productive longer. For, as the labor force figures remind us, the leisure and benefits that so many Americans enjoy depend finally on the fact that a lot of Americans are busy working.