(FORTUNE Magazine) – Remember the Aesop's fable in which the grasshopper plays all summer while the ant works? When winter comes, the grasshopper has no food, while the ant is living it up. It's a perfect parable for retirement investors, and one more of us should heed: The average American sets aside only 5% of his or her income each year for retirement savings, according to Merrill Lynch senior economist Stan Shipley, yet he estimates it would take at least 9% to maintain one's lifestyle at retirement. Over the past few years, this undersaving hasn't seemed to matter. The strong bull market in stocks has bailed many people out, Shipley notes. For the 12 months ended June 30, 1997, the S&P 500 index rose nearly 35%.

You can't count on that continuing. What you can count on, however, is that the very best mutual fund managers will continue to deliver returns that maximize the earning power of whatever you can afford to save for retirement. The tough question is: Who, exactly, are those managers? The ever-expanding mutual fund universe now includes 8,336 funds, according to Chicago research firm Morningstar--an increase of 759 funds since just a year ago. How can one possibly sort through them all?

Don't bother. Because in compiling the following list, we've done the work for you. Our guiding principle was to identify those managers with proven, long-term records in good times and bad. To begin, we asked Morningstar to identify only those funds that have been around for at least five years, because their records would include the rocky market in 1994 as well as our more recent heady times. Then, in vetting the funds, we looked not at absolute returns but at returns adjusted for any sales fees, because those figures more accurately represent what an investor actually gets. We also required that the fund have the same manager for the full five-year period; after all, it's this seasoned experience investors want to tap. Finally, the fund had to be open to new investors; be available in at least 25 states; have a minimum investment of less than $25,000; and hold at least $25 million in net assets. (We excluded nondiversified funds--those invested solely in a single sector, country, or state.)

Our final group is broken down into 16 different categories, from small-company stock funds to corporate bond funds, international stock funds to balanced funds. There are a total of 225 funds in all--just 2.7% of the unwieldy fund universe.

The list itself includes several instructive statistics. First, along with the actual sales load, we've included each fund's annual operating expenses. While these are reflected in a fund's reported total return, they do indicate the minimum threshold a manager must deliver before investors begin to accrue gains. Funds with higher fees will have a more difficult hurdle in slower markets; they may have to take bigger risks to compensate for high expenses.

Second, we've included each fund's one-year return for comparison. This gives an indication of how hot a manager's particular style has been lately. PBHG Growth, for instance, boasts a shining five-year return of 27.8% but is down 10% over the past year.

Finally, we've listed a specific measure of volatility, standard deviation. This statistic shows the range of a fund's historical returns--a standard deviation of 12, for instance, means a fund's returns have fallen within 12 percentage points of the average fund's about two-thirds of the time, and within 24 percentage points 95% of the time. "Steady returns in the past," explains Morningstar's president, Don Phillips, "give fairly steady expectations for the future."

RESEARCH ASSOCIATE Kenji Hosokawa