France has so badly damaged parts of the South Pacific atoll of Mururoa, where it conducts its undergrown nuclear weapons tests, that it may be forced to move the tests to another island in French Polynesia as early as next year.

No decision has been made by France to abandon Mururoa, but nuclear weapons sources in the United States and France have said that test holes already are being drilled in the nearby atoll of Fanga Taufa to see if it can accommodate weapons testing. France conducted its first two underground tests at Fanga Taufa in 1975, before moving the tests to Mururoa.

Sources said the 29 nuclear weapons that France has exploded in the last four years under Mururoa have left the island "looking like a Swiss cheese."

Test holes have been drilled under the 60-feet-deep Mururoa lagoon as far down as one mile into the volcanic rock that underlies the coral-and-limestone atoll. The French have not said when the first test will take place under the lagoon, but it could come in 1981.

France never announces a nuclear weapons test and never confirms one after it takes place. France acknowledges that it conducts occasional tests.

Even the number of explosions France has conducted in Polynesia are supposed to be secret, but U.S. sources place them at 31: two at Fanga Taufa and 29 at Mururoa.

France also keeps secret the size of its tests, most of which it insists are under 20 kilotons.

Sources say that most French tests are engineered to miniaturize their weapons so they can be more easily carried by missiles and aircraft.

The last large French test was understood to be a 200-kiloton test on July 24, 1979. It triggered a small tidal wave, according to the French newspaper Le Matin, when the weapon stuck halfway down the 800-meter-deep shaft leading to the test pit, and way fired in that posisiton.

While admitting the explosion set off a mini-tidal wave, French sources denied that the weapon was struck and denied the explosion took place half-way down the shaft.

One source said the explosion set off an underground landslide of limestone, which lay above the volcanic rock where the weapon was exploded. The source acknowledged that the limestone could have been loosened by previous blasting.

In any case, the earthslide occurred three or four hours after the explosion, when French test personnel had emerged from the bunkers in which they stay during a test.

Less than three weeks before the tidal wave incident, there was an accident on Mururoa involving the handling of plutonium used to make the French explosives. French sources said that an electric drill used to machine the plutonium caused a spark, triggering an explosive chemical fire that killed two workmen.

"It was a stupid accident," one French source said, "but had nothing to do with nuclear testing."

New Zealand newspapers have said the explosion that triggered the tidal wave also vented dangerous amounts of radioactivity to the atmosphere, which French sources also denied.

One source said that most testing on Mururoa takes place in pits about two thirds of a mile down, which he said is deeper than the U.S. tests in Nevada and is more than deep enough to prevent venting. The source said that bubbles of radioactive gas often escape but insisted they are so small and dissipate so rapidly in the atmosphere that they present no threat to the environment.