Japan's defense chief today rejected the most recent American proposals calling for a considerable increase in Japanese defense preparations.

Joji Omura, director-general of the Defense Agency, told reporters after a Cabinet meeting that he would have to reject any plans for military increases beyond Japan's current official plan.

The latest American suggestions, he added, amount to "much more" than the levels set in that plan.

Omura was referring to American suggestions set forth last week at Hawaii, where defense and diplomatic officials from both countries conferred in working-level meetings about Japan's state of military preparedness.

The difense chief's comments seemed to herald a disappointing result in the higher-level meetings later this month in Washington, where Omura is scheduled to meet with Defense Secretary Caspar Weinberger. He said today that he will have to tell Weinberger that Japan will not go beyond current buildup plans.

His remarks also represented another step away from the generalized promises that Prime Minister Zenko Suzuki had made during a state visit to Washington last month, when he pledged Japan would make greater efforts in the defense field.

The meetings in Hawaii and Washington had been planned to work out details of what once appeared to be a greater Japanese military commitment in light of the Reagan administration's desire for an allied response to Soviet military advances.

But since the Washington summit, Suzuki has backed off, claiming that he had not promised any new commitments in his meetings with Reagan. He also has fixed a budget limit for next year that leaves little financial room for higher defense spending.

Omura confirmed today that the U.S. side in the Hawaii talks had expressed displeasure with the recent Japanese Cabinet action setting a limit of 7.5 percent on defense spending increases next year.

Yesterday, Chief Cabinet Secretary Kiichi Miyazawa reiterated that there would be no change in the limit of 7.5 percent for next year's budget.