WASHINGTON (AP) _ Business executives testified Tuesday in favor of proposed revisions in U.S. trademark law that would allow them to apply for trademark registration before new products are marketed, as foreign companies are allowed to do.

Debra Fields, president of Mrs. Fields Inc. of Park City, Utah, which owns Mrs. Fields Cookies, praised the bill for proposed elimination of an ''expensive and time-consuming'' requirement that a trademark be used in interstate commerce before an application for registration can be filed.

''The new law will eliminate expensive business risks which small businesses can least afford to take,'' she said.

She noted that small businesses risk losing thousands of dollars in wasted effort by designing and labeling a trademark for token marketing of an experimental new product in another state, only to discover that the trademark already was registered by another company.

The bill would allow U.S. citizens to apply for registration of their trademarks before product plans have been completed.

''It's disturbing that U.S. law currently gives foreign trademark owners an advantage that U.S. businesses do not have,'' DeConcini said.

The statutory revisions also were endorsed by Ronald R. Kranzow, vice president of Frito-Lay Inc. of Plano, Texas; C. DeForrest Trexler, deputy general counsel of Mack Trucks Inc. of Allentown, Pa., and Herbert A. Hedden, assistant director of the International Franchise Association.

The corporate witnesses also supported the bill's provisions for removing old trademarks that already are being used, and for prohibiting ''dilution'' of famous trademarks by non-competing manufacturers.

As an example of dilution, Trexler cited an instance when a manufacturer of men's undershorts tried to used the Mack Trucks bulldog trademark on its products. Such practices are forbidden by 23 states but not under federal law.

DeConcini said U.S. corporations and business organizations, including the Chamber of Commerce of the United States, PepsiCo Inc., Amoco Corp. and Hasbro Inc., also had expressed support for the first major revisions in trademark law since 1946 to remove ''cumbersome and uneconomical filing procedures.''