The definition of an optimist, it's been said, is an accordion player with a pager. Or a Cubs fan with World Series tickets.

Most investors are also optimists. They're making a long-term bet that the value of their stocks or mutual funds will rise, at least enough to stay ahead of inflation.

But with the inflation rate rising and the stock market shaky, even the most optimistic investors are finding it hard to be cheerful. Unless, that is, they own inflation-adjusted Savings Bonds, or I Bonds.

The interest rates that I Bonds pay include two components: a fixed rate that stays the same for the life of the bond, and an inflation rate that's adjusted every six months. The inflation rate for I Bonds issued in May, based on the change in the consumer price index between September 2007 and March, will jump to 4.83 percent from 3.06 percent. If you already own I Bonds, your new rate will range from 5.83 percent to more than 8 percent, depending on the fixed rate for your bonds.

And if you're considering buying I Bonds? Analysts recommend buying before May 1, even though that means you'll have to wait until October to receive the inflation-adjusted bump in rates.

Here's why: By purchasing I Bonds before May 1, you'll lock in the current fixed rate of 1.2 percent, says Daniel Pederson, author of "Savings Bonds: When To Hold, When To Fold, and Everything In-Between." Pederson believes Treasury will lower that fixed rate on May 1. Treasury doesn't announce its plans for the fixed rate in advance. But in the past, Pederson says, whenever the inflation rate on the I Bond has risen sharply, the Treasury has cut the fixed rate.

Since I Bonds were introduced in 1998, the lowest fixed rate Treasury has set for I Bonds is 1 percent. But in May, Treasury could cut the fixed rate to 0.5 percent or even lower, predicts Tom Adams, author of "Savings Bond Advisor." In the past, he says, Treasury has set the fixed rate about 1 percentage point below the rate for 10-year Treasury Inflation-Protected Securities, or TIPS. The current rate for 10-year TIPS is 1.25 percent.

If you buy I Bonds between now and May 1, you'll receive a combined rate of 4.28 percent until October. But then comes the payoff: The May inflation adjustment will kick in, and you'll earn 6.06 percent for the next six months.

More important, you'll guarantee that your I Bonds pay a fixed rate of 1.2 percent for as long as you own them. Though the rate for I Bonds bought after May 1 will look appealing at first, Pederson says, "The fixed rate is what people should be keeping their eye on."

HIGH-YIELD BONDS

If you already own I Bonds, you'll see a rate increase, but it won't necessarily happen on May 1. New rates take effect every six months, based on the month in which your I Bond was issued. If, for example, your I Bond has a January issue date, Pederson says, the rate increase for your bonds won't kick in until July.

The rate increase is worth waiting for, especially if you bought an I Bond between 1998 and 2001. I Bonds issued in those years carry fixed rates of 3 percent or more.

When the new inflation rate kicks in, those I Bonds will earn a combined rate of up to 8.5 percent, Adams says. Returns from other conservative investments don't even come close.

In addition, I Bonds are exempt from state and local taxes, and you don't have to pay federal taxes until you cash them in.

PURCHASE LIMITS

Keep in mind that the inflation rate is adjusted semiannually. If consumer prices ease in the next six months, your rate will drop. That may be a risk you're willing to take. But here are some other potential pitfalls you should be aware of before you invest in I Bonds:

I Bonds aren't as liquid as short-term CDs or high-yield savings accounts. You can't redeem an I Bond until you've owned it for at least a year. And if you cash an I Bond within five years, you'll forfeit the three most recent months of interest.

There are limits on the amount of I Bonds you can buy. As of Jan. 1, the maximum amount of I Bonds an individual can buy in a calendar year is $5,000, down from the previous limit of $30,000. Treasury said the change reflects the original purpose of the Savings Bond program, which is to make Treasury securities available to people with relatively small sums to invest.

The maximum applies to each I Bond format, so you can double your limit by buying $5,000 in paper I Bonds and $5,000 in electronic I Bonds.

Treasury bases the limit on an individual's Social Security number, so a couple could buy up to $20,000 in I Bonds a year by purchasing the maximum in paper and electronic form.

For more about I Bonds, go to the Treasury's Web site, www.treasurydirect.gov.