NEW YORK (AP) _ Big earners who find life a bit more taxing this year may want to consider investing in bonds that do a better job of protecting their income.

It's too late to minimize one's tax liabilities in time for April 15. But this year's combination of lower interest rates on bonds and higher income taxes for some earners is making tax-free investments more attractive in 1992, tax experts say.

Interest earned on municipal bonds, for instance, is not only free from federal income taxes, but also shielded from state and local taxes if the buyer lives in those localities.

''The after-tax benefits of munis for a person in a high income bracket are remarkably attractive this year,'' said Michael Hardie, who manages $3.5 billion in municipal bonds as director of tax-free bonds at Colonial Mutual Funds.

Consider a buyer of a 7 percent bond free of federal taxes. If that investor is in the 31 percent federal-income tax bracket, his or her equivalent taxable yield is 10.14 percent, said David Rievman, a tax associate at Skadden, Arps, Slate, Meagher & Flom, a Manhattan law firm.

For middle-income investors taxed at the 28 percent federal level, the effective yield is 9.72 percent, Rievman said.

Long-term Treasury bonds, which are taxable, currently yield only about 7.75 percent.

''The higher your income tax rate, the more advantageous it is to invest in municipals,'' Rievman said.

Of course, municipal bonds are considered riskier than Treasury bonds, since the probability of the federal government defaulting on interest payments is far less likely than that of state and local issuers.

If issuers miss interest payments on bonds, funds that invest in those bonds typically show declines in principal as well as interest.

While it's too late for bond investors to benefit from tax-free investments in time for April 15, there is still time for some to take advantage of a rule clarification.

Last July, the federal government said it would give a break to investors who recently exchanged their corporate bonds for newly issued bonds. Such exchanges typically occur during restructurings of corporations unable to handle debt payments.

The rule allows investors who bought new bonds after July 11, 1991 to amortize the difference between new bond's face value and its market value.

For example, if the new bond is worth only 70 cents on the dollar, ''the 30 cents can be deducted over the life of the bond,'' says Rievman.

Other tax advantages can be reaped simply by paying more attention to existing rules.

For example, some bond buyers forget to deduct interest they had to pay to the seller of the bond. If, for instance, the investor buys a Treasury bond three months after its most recent semi-annual interest payment date, he or she pays the seller interest that would have been earned during those three months.

''Invariably (buyers) always forget to deduct this accrued interest on purchases,'' said Herman Schneider, national tax director for the securities industry at Coopers & Lybrand, the New York-based accounting firm.