For example, when you buy a policy, you may ask your agent, "How much of the premium cost is paying for the insurance portion and how much will be invested?" Chances are, the agent can't tell you; he or she can guess, but the answer cannot be determined until a year after you buy the policy.

In addition, your agent can guess--but won't know for sure--what rate of return you will earn on the invested portion of your account or how much of the money is earning interest.

And although somebody at the company that wrote your policy will eventually determine the answers to these questions, he or she is not likely to tell you--even after you've become a policyholder.

"Once a year, they'll tell you what your policy's cash value is, and they'll tell you how much you need to pay in premiums--they don't want any confusion about that," says Joseph Belth, a professor of insurance at Indiana University and author of "Life Insurance: A Consumer's Handbook," published by Indiana University Press.

Other than that, much about the policy is not disclosed.

"Whole life is kind of funny. It's like mechanics inside a bag," says John A. Kiczek, an analyst in the life and health division of A.M. Best Co., an Oldwick, N.J.-based firm that tracks insurance information. "You can't just look at it and see what's where. But if you try really hard, you might be able to figure it out."

A few things are clear. Premium payments for this type of insurance are a constant. If they start at $2,000 a year, that's what you'll pay when you're young and it's what you'll pay when you're old. If you can't pay the premium in a given year, the policy will lapse and you'll get the cash value back, minus any cancellation fees.

In addition, with whole life you are likely to lose the full amount of premiums you've paid if you cancel in the early years of your policy. That's because the cost of writing these policies--the agent's commission, the underwriting fees and expenses--are front-loaded.

The cash value of your whole life policy in the first year is likely to be zero. And for the first several years, it is likely to remain a fraction of what you've paid in premiums. About 17% of whole life consumers cancel within the first two years, according to the American Council of Life Insurance in Washington.

This type of insurance was created to fill a specific need. Many people require insurance for just a few years--perhaps when they have a young family that relies on them for financial support. Others need insurance for a long time--perhaps their entire lives--possibly because they're supporting a disabled child or a nonworking spouse.

For younger people, buying inexpensive term insurance makes sense. But buying term insurance when you're older can be prohibitively expensive. That's because insurance pricing is based on statistical averages that indicate how likely it is that the policy will pay out a death benefit in a given year. When all policyholders in your statistical group are young and healthy, the chance of anyone dying is low, so the premiums are low. The older you get, the more likely the chance of death, and the higher the annual premium.

Insurance companies designed whole life to cover consumers for as long as they live or to age 100, whichever comes first. (When these policies were conceived, few people lived to 100. Now, however, some companies are revamping their policies because such longevity isn't as rare.) If the policyholder lives to 100, he or she receives an amount equivalent to the death benefit. (By the way, this payment isn't necessarily a good thing; it triggers a tax obligation that can be onerous.)

These policies compensate for the problem of insurance costs rising with age by having you overpay in the early years of the policy. And the amount that wasn't needed to cover "mortality fees"--the cost of paying death benefits to the heirs of the few people in your group who died--is invested and becomes the "cash value" of your policy. The cash value becomes a financial resource you (or your heirs) can tap.

The amount of insurance you need is determined by the gap between the resources you have and those your dependents will need in the event of your death, so the cash value of your policy reduces your insurance need. As time goes on and the cost of insurance rises, you buy less and let the cash value take on a bigger role.

If you die, a portion of the death benefit paid to your heirs would come from pure insurance, while the other portion would come from the cash value--the invested amount--of your policy.

The biggest problem with whole life insurance is that you never know how fast the invested portion will grow, because you don't know in advance the rate of return you're earning on your money, nor how much of your money is invested.

On some policies, the cash value grows fairly rapidly and the insurer pays a decent return on your money, making it a comparatively good buy. On others, the cash value edges forward at a snail's pace and the return on your money is paltry. But you won't know that when you're buying the policy.

In fact, your insurer will give you just one guarantee on the investment portion of your policy: The cash value will earn interest of at least "the guaranteed rate," probably 3% or 4%. As investments go, that's not much of a return. So if that was all the policy had to offer, few people would buy one.

Most insurers pay more, but they won't tell you in advance how much more. They'll illustrate what would happen if the policy paid out each year what it's paying today. But the chance of the return remaining constant at today's rates is practically nil.

Now, mutual funds can't--and won't--make promises about future investment returns, either. But what mutual fund companies do--and insurers usually don't--is give consumers a detailed look at the fund's past returns.

Trying to get that information from an insurer or insurance agent requires an unusual amount of perseverance--and often the patience of a saint, Belth says. Often agents and insurers flatly refuse to provide that kind of detailed data.

"The insurance industry has evolved over a 150-year period as a nondisclosure industry," Belth says.

But the good news is that you don't have to get this information from an insurer. You can get it from A.M. Best. If you're shopping for a whole life policy, take a look at Best's Policy Reports, which are available at your local library. "Whole Life: With Dividend Histories" and "1997 Historical Supplement: 10- and 20-Year Whole Life Dividend Performance" are two reports that are especially useful for whole life buyers.

These books allow you to shop for a policy in the same way you'd shop for a mutual fund.

The product specifications section in "Whole Life: With Dividend Histories" spells out limitations and details of each insurer's whole life policy.

"Historical Supplement" shows the past performance of each policy. It includes ratios you can use to figure out how much a policy would cost; how much your cash value would have grown over time; and the average policy cancellation, or "surrender," fees. And it shows what the company's sales projections were--the rates of return it told prospective customers they were likely to earn--in the past versus what they actually earned.

* * * Adapted from "Kathy Kristof's Complete Book of Dollars and Sense." Printed with permission of Macmillan Publishing, New York. Write to the author in care of Personal Finance, Business Section, Los Angeles Times, Times Mirror Square, Los Angeles, CA 90053, or kathy.kristof@latimes.com. KATHY M. KRISTOF welcomes comments and suggestions for columns but regrets that she cannot respond individually to letters and phone calls.