American Century Twentieth Century Giftrust is in a wicked slump following more than a decade of stellar performance.

Giftrust, 1-800-345-2021 or (www.americancentury.com) has been a superb place to stash money for a young person's future. You can invest money only as a gift to someone else, and the money must stay invested for at least 10 years or until a child reaches majority, whichever is longer.For the first 12 years of its life, through the end of 1995, Giftrust returned an annualized 22.1 percent, making it a perennial top performer among aggressive-growth funds. In fact, it was one of the best performing of all mutual funds during those years.

But in 1996 and 1997 Giftrust went on the fritz, finishing in the bottom 10 percent among its peers both years.

Robert Puff Jr., American Century's chief investment officer, reports that some investors grew so worried that they wrote to get their money out before the required period had elapsed.

For the most part, Giftrust is being hurt by the same investment methods that have served it so well at other times.

It practices "momentum investing" - that is, it buys small companies whose rates of earnings and sales growth are accelerating, and it pays no heed to such signposts of value as price-earnings ratios.

Since mid-1996, speculative fever in such stocks has been absent, and other momentum funds, such as those run by the PBHG and Van Wagoner fund families, have done just as poorly.

Puff concedes that his managers contributed to the debacle, though. Specifically, Giftrust shunned financial stocks, despite their fast-growing earnings.

Moreover, "we had some explosions," he says, referring to plummeting share prices of stocks that failed to meet analysts' ex-pec-ta-tions.

Giftrust, he says, was often too slow to sense trouble.

"We didn't always respond at the crack of the bat," Puff says.

The workload of Giftrust's managers has been lightened in an attempt to remedy that situation.

Last year, Glenn Fogle and John Seitzer ran Giftrust and Vista, which performed even worse than Giftrust. This year, Chris Boyd has returned to the firm to manage Giftrust with Seitzer. And Fogle runs Vista with newcomer Arnold Douville.

Puff is confident that momentum investing will come back in style and carry Giftrust along with it, sooner rather than later.

"If it doesn't," Puff adds, "you might be talking to someone else next year."