Japan today gave ground on an issue that it has debated with the United States for more than a year: the protection of computer software from unauthorized copying. The action apparently was taken to defuse growing trade tension with the United States.

Japanese officials told U.S. trade negotiators that the government soon will submit legislation specifying that software qualifies for 50 years' protection under Japanese copyright laws.

That put an end to a proposal floated by the Ministry of International Trade and Industry (MITI) to treat software as an industrial product and subject it to patent law, according to Japanese officials.

In Washington, U.S. Trade Representative William E. Brock expressed "pleasure" at the Japanese move and said in a letter to MITI Minister Keijiro Murata, "It is of major importance that Japan has recognized that copyright is the appropriate form of protection for software."

Under MITI's plan, protection was to be limited to 15 years and, in special cases, the government was to be empowered to force companies to license software that they did not want to sell in Japan.

Washington consistently has pushed Japan to apply copyright laws to software, as is done in the United States and many other industrialized countries.

A U.S. official here called the Japanese move today "a welcome development," but said the United States had not yet seen the fine print of the Japanese proposal and continues to have concerns over the MITI idea.

But a Japanese foreign ministry official said U.S. apprehensions "will disappear." In addition to the patents approach, Japan has dropped plans for compulsory licensing and registration, he said.

Software is the complex programming that controls a computer's operation. Many companies using computers spend more on it than they do on the machines themselves.

The United States is generally held to have an edge over Japan in the field and, having relinquished leadership in so many others, is anxious to preserve it.

The patent-vs.-copyright debate is highly technical, but U.S. officials maintain that it holds a key to whether foreign companies can profitably market their best wares here.

In recent years, Japanese courts have ruled that software is covered by existing Japanese copyright laws, according to Japanese officials. But manufacturers complain that, in practice, protection is ineffective and pirating common. A year ago, at least 44 lawsuits were pending.

MITI's proposal, which appeared in 1983, depicted patent protection as a way of filling gaps in the existing system. In any case, it argued, 50 years of protection is too much in a field that is changing so fast.

The change also would have brought the field under the control of MITI, rather than its bureaucratic rival, the Ministry of Education, in which the copyright office is located.

In addition to the shortened term, U.S. manufacturers were wary of MITI's suggestions that the law might give the government a sort of eminent domain over all software of companies doing business here.

Under this plan, if it were deemed to be in the national interest, the government could have forced the licensing of programs which, for whatever reason, the owner did not want to sell in Japan. The foreign companies also objected to Japanese proposals that key data about their software be placed on file with the government for use in the event of litigation.

Foreign software producers and the U.S. government argued that software is "intellectual property" like a novel or play and deserves the 50-year protection normally given such works.

The debate reached a peak a year ago, with the United States taking an unusually high-profile stance. It then subsided as the Japanese government agreed to shelve the MITI proposal for the time being.

Today's statement was the firmest assurance the United States has received that the idea will not be adopted. The new law, which probably will be introduced later this year, will strengthen protection by specifying that software is protected, according to Japanese officials.

Earlier, Japan announced plans to enact a separate law to protect designs of computer chips, another product that has tended to fall through the crack separating patent and copyright laws.