As more women take careers, they're plunging into estate planning

You're a busy career woman, coming home each day after a hectic 10 hours to feed and clean up after the kids before you can sleep. You don't have much of an estate to leave to your heirs, or time to plan it. So why should you bother?

Most people are motivated to plan their estate when they find out exactly what would happen if they didn't, says Dixie Johnson, a cooperative extension specialist in consumer economics at Purdue University. Then they realize they lose the choice as to how their assets will be distributed if they leave it up to the state.

Estate planning will also ensure that more of your money goes to your heirs by reducing estate taxes. ''The IRS benefits from the tax saving plans you don't make,'' notes Stephen Leimberg, professor of taxation at American College in Bryn Mawr, Pa. Although they rarely do so, the rich can afford not to plan and to lose money, he continues; the middle class cannot.

Today, estate planning is as vital for an increasing number of women as it always has been for men. More women, as divorce has become more common, have the sole responsibility for providing for their children. As more women have moved into the work force and into higher paying jobs, they have preserved more assets - a house, investments, and CDs - to pass on to those children.

First of all, consider saving taxes by reducing your estate. The fewer dollars over the current tax-free deduction of $325,000 in your estate during probate, the fewer tax dollars will be paid by your family and friends. Don't give away anything you think you might need, advises Wayne Dziedzic, an estate planner at Cambridge Group in Newton, Mass., but you may give up to $10,000 to each potential heir each year free of gift taxes, or a couple may give $20,000 per recipient. Another advantage of lifetime giving surfaces when the recipient is a minor child with little or no additional income. Future interest earned by the gift will be taxed at a very low rate or not at all.

You may leave the entire balance of your estate to your spouse tax-free, because of the unlimited marital deduction provided for in the Economic Recovery Tax Act, says Dale Bizzi, an estate planner at State Street Bank in Boston. Because of this provision, you now have a particularly good reason to follow the experts' advice to update your will every three to five years. If it was drawn up before Sept. 13, 1981, and cites the estate law current then, it may qualify your estate for only half the legal marital deduction, warns Mr. Leimberg.

There is one simple step that you can take now that will save your heirs endless hours and possibly thousands of dollars, he continues. Put your important documents - car title, house deed, will, and social security information - in a safe deposit box. More than one person should be authorized to open the box. Also, store the name and phone number of your banker, fire insurance agent, accountant, etc. in the box. A copy of the will should be kept elsewhere, perhaps in a fireproof box at home.

Here's the scenario: You would like to make sure the estate you inherited from your first husband goes to his children. Yet you feel your second husband may need some of the money to raise those youngsters. Since Jan. 1, 1982, you could set up a QTIP (qualified terminable interest trust) leaving the interest to your second husband, but preserving the principal for the kids. QTIPs have become very popular in these times of many second and third marriages, notes Ms. Bizzi.

Many people proclaim ''I'm too busy to plan,'' says Mr. Leimberg, and by their inaction shift the burden to others who are not as capable of preserving the large sums of money they may inherit - such as life insurance benefits. If your heirs are inexperienced in investing money or you want to make sure your children don't spend all their inheritance on a Maserati, you may want to set up a trust for them. In addition to a knowledgeable and competent trustee from a bank or financial institution, you will want as co-trustee a close friend who has views similar to yours - and will probably make decisions about your estate similar to your wishes.

How much life insurance do you need? The purpose of life insurance is to provide financial security for your dependents and especially to hold them through the probate period, before they can get money from the estate. Make sure that it is enough that property need not be sold at a loss to meet tax expenses, Mr. Leimberg says.Most experts advise buying life insurance worth between three and five times your salary. However, if a lot of liquid assets are available you may not need as much.

Mr. Leimberg's formula: Multiply current living expenses by 75 percent. Divide this by 7 percent (a safe estimate of average interest) and subtract capital on hand. This equals the life insurance you need. A life insurance policy can also be set up to fund a trust.

The needs of your heirs may be very different. Your state's distribution may be equal but not equitable; a special child or a child in school may need more than a daughter who is established in her own career, Leimberg advises. If you don't record your wish to leave some money to your church or alma mater, or even a home for retired horses, for that matter, it won't happen.

As executor for your will, choose someone you can trust who can handle complex business matters. Be sure to specify backup executors, backup beneficiaries, backup guardians, and backup trustees in the will.