President Reagan signed legislation this week that clears the way for the United States to enter into a treaty giving reciprocal copyright protection to American artists and writers and those of 76 other countries.

For those in the U.S. who make a living at selling creative works, the treaty is a welcome milestone that was much too long in coming.The original treaty, called the Bern Convention for the Protection of Literary and Artistic Works, was first signed in 1886. Differences between American and other nation's copyright laws have stalled ratification for more than 100 years since.

While treaty participation will give the United States copyright relations with 24 countries with which it has had none, it is still only an initial step. Those nations must now act to halt pirating of U.S. books, movies, videos, recordings and artistic works that takes place within their borders.

Across the world, American creative works are used without fair payment. Tapes and records by American musicians are copied by the thousands and sold cheaply. Pirated American television programs picked off satellites by television stations in South America, and Asian publishers reprinting American college texts without permission are only a small example of this widespread problem.

Clearly, the treaty is not going to solve the entire problem of a black market in copied music or books. But it is a necessary beginning.

The U.S. government should get tough on countries where such abuses are found. It should use appropriate leverage, including the new treaty if it applies in the violating country, to force royalty payments.

Stealing something just because it is easy to copy or pick-up on the nearest satellite dish should not be tolerated.