WHEN THE SENATE Labor and Human Resources Committee held its first hearings last week, under the chairmanship of Sen. Orrin Hatch, the subject was women and work. While expressing disagreement with Sen. Hatch's views on ERA and affirmative action, many of the witnesses from the various women's organizations later expressed as well both surprise and relief at the chairman's stated intention to "establish a dialogue with all working women."

Quite apart from the practicality of establishing good relations with a vocal interest group, there are solid economic reasons for Sen. Hatch's interest. Women now constitute 43 percent of the labor force, and they appear to be in it to stay. Most of the women who work need their jobs. An increasing number, at all income levels, are the sole or main support of their families. For them, the real choice is often between work and welfare. Even in families with two or more earners (the rule now, rather than the exception), the earnings of the wife have come to be relied on to provide things -- such as a college education for the children -- that are no longer considered a luxury.

Not only do women need work, but the economy needs their contributions. One obvious reason is the growing proportion of the population that is elderly. Without the taxes paid by working women now and in the future, the Social Security trust fund would be in much greater trouble than it is already projected to be.

Women are a major source of the economy's strength. To some extent, this contribution is distorted by two of the most familiar indicators used to gauge the economy's health. Having more women in the labor force has tended to increase unemployment and reduce productivity as these are traditionally measured. Women who are not the sole or major support of dependents have greater freedom to change jobs and search at length for work. And they usually have more demands on their time for household chores and child care. In recent years, many have begun looking for jobs for the first time or after long periods of remaining home.

All of these factors will increase measured unemployment among women (although, mostly as the result of recent sharp increases in male unemployment, the rates for men and women are now very close). Because new workers are usually less productive than experienced ones, and because women tend to be segregated in low-paying service jobs, more working women has also meant lower output per worker-hour, the traditional productivity measure.

These factors are likely to decline in importance as women gain experience and move to more stable, better-paying jobs. But even if this doesn't happen, measured unemployment and individual worker output are not the only, or even the most important, indicators of economic performance. What really determines the wealth of the nation is the total amount of goods and services available to each citizen, whether working or not. And by this mesure, the nation is vastly better off for -- and highly dependent on -- the efforts of the 45 million women who are now in the country's work force.