American trade officials said today that Japan had granted virtually all their requests in negotiations aimed at opening this nation's markets further to foreign radio equipment and services.

"We are very pleased with the results," Clyde V. Prestowitz, counselor to the U.S. secretary of Commerce, told reporters here. "We feel we accomplished what we set out to accomplish.

"The result, we think, will be a more open market and, we hope, more business for U.S. companies," Prestowitz said. But he said it was impossible to put a dollar figure on the changes.

The talks, which began late last spring, focused on sales of radio telecommunications equipment such as pocket pagers, car telephones and mobile data transmitters in Japan, and on foreign companies' freedom to offer services using such equipment.

In the talks, Japanese officials agreed to simplify standards by which equipment is certified for sale in Japan and to accept foreign test data. The United States maintained that current procedures are a barrier to trade.

The Japanese also agreed to open certain radio service fields that previously were closed to foreign companies. The licensing of transmitters and assigning of frequencies would be conducted openly and impartially, they said.

The negotiations were concerned only with point-to-point communications using radio, and not with the operation of mass-media radio stations. Some of the new steps will require the approval of the Japanese Diet, or parliament, where delays or rejection are possible but not expected. Others can be accomplished by rewriting regulations.

But with many details remaining to be worked out, some Americans involved in the field are reserving judgment.

Japanese officials said tonight it proved they are serious about settling trade tensions.