Brazil took another step toward easing trade tensions with the United States this week by officially barring production of a personal computer alleged to be an illegal copy of Apple Computer Inc.'s popular Macintosh.

Meanwhile, Brazilian manufacturers were warned that a new U.S. trade bill being considered by Congress could weaken the presidential authority on trade that helped Brazil during recent bilateral trade organizations.SEI, the government's computer development regulatory agency, published a notice Monday in Brazil's public register, officially withholding approval for Unitron Engenharia Industria e Comercio Ltda. to manufacture its 32-bit personal computer.

SEI said in the announcement that it vetoed the project because Unitron, based in Sao Paulo, attempted to market the computer without SEI authorization.

Last year Unitron offered a few units of its MAC-512 computer for sale to the public without waiting for SEI approval.

The company opened itself further to accusations of piracy by marketing the MAC-512 machines with a copy of the Macintosh operating program in the absence of its own software, which Unitron said would be made available later. Mac is a popular nickname for the Macintosh.

SEI director Jose Ezil Veiga da Rocha denied that the decision had anything to do with recent Brazilian government efforts to mend tattered relations with Washington, which has threatened trade sanctions.

Unitron has been accused of illegally copying the Apple Macintosh since the SEI began examining its project almost two years ago. Apple Computer, of Cupertino, Calif., threatened to sue if the computer went into production.

Unitron announced that it will contest the SEI decision.

Mr. Veiga da Rocha said his agency might reconsider its decision if Unitron redesigned aspects of its project that most flagrantly copy the Apple product. However, he said that reopening the case would not be easy.

Meanwhile, Brazilian businessmen were advised that the trade bill being considered in Congress would strengthen that group's powers as well as the power of the U.S. Trade Representative's Office to impose sanctions for unfair trade practices.

At the same time, the trade bill also could weaken presidential discretion to impose, withhold or drop retaliatory measures.

In the confrontation over Brazil's closed computer market, the White House several times has postponed threatened sanctions in order to give the Latin country time to modify its policies.

Currently, threatened USTR sanctions against Brazilian exports have been shelved pending approval of new Brazilian computer software marketing laws.