The Philippine government is rushing its safety probe of an American nuclear power plant being built on the slope of a volcano in order to weaken opposition to the reactor, a Philippine opposition leader charged yesterday.

Lorenzo Tanada told a news conference in Washington that the "hasty and hurried" hearings of a special commission showed that the group "is interested if finishing the job, not in doing a good job."

Tanada was offered the job of heading the commission, which President Ferdinand Marcos named in the wake of the Three Mile Island accident in Pennsylvania. However, Tanada said, he turned it down because he lacks impartiality in the matter.

Tanada and others have criticized the planned nuclear plant as sitting on top of an active earthquake zone and too near Mount Natib, an inactive volcano that may only be dormant. They have also charged that the Westinghouse design is faulty. The company maintains that both its equipment and the site are safe.

The case has become something of a test of U.S. policy on nuclear exports, which have traditionally involved only an assessment of risk to American national security and no evaluation of environmental effects. That aspect has been left to the foreign governments as their sovereign right. Marcos suspended reactor construction pending his commission's report.

Permits to export the 626-megawatt reactor and other parts have been pending before the State Department and the Nuclear Regulatory Commission since 1976. The permits should not be issued, Tanada said. He plans to take U.S. nuclear safety experts back with him to the Philippines to testify before the commission.