If you are a working woman, chances are that a certain portion of your paycheck vanishes every week into the Social Security fund. Chances are, too, that you expect that money to reappear in the form of benefits once you reach the age of 65. You may well be thinking that the more you earn now, the better off you are going to be when you are on Social Security. If you are married, think again.

The way that benefits are presently calculated, according to Rep. Mary Rose Oakar (D-Ohio), chances are that you won't get any more than if you had never worked at all.

"Your husband's salary is typically higher than yours," she says. "So your credits don't count for anything. You take the dependent spouse benefit, but here you've paid all these credits in" over the years and you get nothing back for it. "If you put in all the credits you put in and he put in, you'd get much higher benefits."

Oakar has proposed an "earnings sharing" approach in the Social Security Modernization Act to correct several aspects of the system that discriminate against women and married couples. Oakar, who is a member of the Select Committee on Aging, says the legislation evolved out of a report done by the Carter administration that identified discriminatory aspects of the system. The system was set up in 1936 to cover a male breadwinner and a dependent spouse, the typical family structure of that time.

"In 1936 the demographics of the country were very different," Oakar says. "Only 15 percent of women worked. Today nearly 70 percent of women work part- or full-time. They didn't anticipate women would be working.

"What an earnings sharing approach does is take my credits, his credits and recognizes equal contributions made to the marriage by each and splits them in half."

Right now, she says, the average benefit for a woman is $390 a month and for a man it is $500 to $510 a month. Under an earnings sharing approach, the benefit for a working married woman would increase an average of $160 a month to $550. The married man's benefit also would rise to $550. Men whose spouses make more than they do also would benefit.

"For the vast majority of women in the years ahead, Social Security is going to be pretty much it for them," says Oakar. "We've taken away the IRA {Individual Retirement Account} breaks, we've taken away many incentives to save for a pension. In Sweden the older people are the richest. In our country, Social Security is it. So we better make sure it is fair."

Another provision Oakar wants to reform would benefit homemakers. "Their problem is that the woman is much more likely to go in and out of the labor force to take care of kids and sick parents." If that homemaker becomes disabled, however, and she has been out of the work force more than five years she is not eligible for disability benefits. Oakar says her office has heard from a number of women with multiple sclerosis who cannot get disability benefits. "No homemaker can get disability insurance from a private firm," she says. Under earnings sharing, whatever the husband earns would be divided in half for purposes of determining the wife's disability eligibility.

Earnings sharing also would help divorced homemakers who were married less than 10 years by allowing the former husband's contributions to Social Security during the period of marriage to be factored into the woman's benefits later on. Now a divorced woman must have been married at least 10 years before her contributions to a marriage are recognized in calculating her Social Security benefits.

"The point is that working spouses have a problem, divorcees married less than 10 years have a problem, and homemakers have a problem," says Oakar. "I've introduced this since 1979 and now is a prime time to do something about it. Social Security has a very nice surplus in it. It's doing real well and collecting 7 percent interest on the investment. They've got the money to phase in these changes and correct the system."

Projections call for a $400 billion surplus by the year 2000, she says. The estimated cost of revisions is $75 million a year.

The poorest people in the country are elderly women, she says, partly because of the way Social Security is calculated and partly because they earn less than men when they work. "The poverty rate for older women is twice what it is for men. They are 72 percent of the elderly poor. It's something younger women should be very concerned about. The fastest-growing population in the country is over 85. The bad news is that when you live longer, you become more poor than when you're younger. That's why . . . Social Security is so important to reform."

And to understand.