Millions of working women and their families have just received a long-sought benefit from Congress which saves them money and adds tremendously to their job security. A new law makes it illegal to discriminate against a woman worker when she's pregnant.

In detail, this law adds up to a sweeping bill of rights for employes of childbearing age. Effective immediately, a company can no longer:

Deprive a woman of seniority rights, in pay or promotion, because she took a maternity leave.

Treat a woman back from maternity leave as if she were a new hire, having to start all over again on the eligibility period for pension and other benefits.

Force a pregnant woman to leave a job before she wants to go.

Refuse to hire a woman just because she's pregnant, or fire her for the same reason.

Another important benefit - equal access to various forms of health insurance - will follow early next year. Starting April 29, 1979, employers may no longer:

Refuse to cover an employe's normal pregnancy and delivery expenses in the company health plan, or pay less for pregnancy than for ever, they still exclude abortions.)

Refuse to pay sick leave or disability benefits to women whose difficult pregnancies kept them off the job.

The only women not covered by this law are those who work for companies with fewer than 15 employes. In other type of public or private employment, your equal rights are now guaranteed.

Until now, the legal status of pregnant women in the work force had been ambiguous. A recent Supreme Court decision said that women on maternity leave couldn't be stripped of their seniority rights. But an earlier decision okayed the corporate habit of excluding pregnant women from disability plans.

Several states have mini-bills of rights, and some companies did the fair thing voluntarily (or at the strong suggestion of the Equal Employment Opportunity Commission). But more women than not were out in the cold.

This hodgepodge is now behind us. The law makes a clear statement that workers can't be excluded from company benefit plans solely on the ground of pregnancy.

Companies may still choose to do without plans entirely - and in fact many smaller companies offer no health or diability benefits to any of their workers. But where plans exist, pregnant women must be covered.

The new access to disability plans is a special comfort to women who have trouble with their pregnancies. In the past, you had to drag yourself to work or lose your paycheck. Now, if the doctor orders you to bed, you can continue to receive your salary under the company disability plan, just as you would if you'd suffered a back injury or a heart attack.

Big companies may offer disabled workers six months or more of full pay. If you had to leave work in your seventh month, and weren't fit to come back until two months after the delivery, you might receive you regular paycheck for that entire period. (There's no payment, however, if you're able to work, but choose to stay home for an extra month with your new baby.)