A CARTOON in a recent Sydney tabloid describes the French nuclear-test site at the atoll of Mururoa as ''France's latest South Pacific resort.'' The picture is complete with sunbathers basking in antiradioactive gear under a nuclear mushroom cloud. The French commanders on Mururoa - about 4,285 miles east of Sydney and 11,178 miles from France - would not be amused. The perception of the site as riddled with radiation is one they are eager to dispel as protests mount against France for resuming underground nuclear testing in September. ''You will see some 1,500 people living here, without radiological restrictions,'' Gen. Paul Verical, military commander of the nuclear-testing site, tells visiting journalists. ''In the middle of the South Pacific ocean, we are in the largest desert of earth,'' he adds. ''We are very far from the principal countries. We are also very far from our mother country.'' From the air, Mururoa looks like a sinuous ring of earth, surrounding a delicately colored lagoon, and lost in Pacific vastness. This is one of the largest atolls in the South Pacific, about 17 miles long by 6 miles wide. Its coral rim is about 10 feet above sea level. According to French officials, it is the most studied point of land on earth. About 6,000 samples of water, soil, plant, and fish life are taken every year, in addition to regular tests for radiation. On the ground, the atoll is an often surreal mix of massive concrete structures, rusting cables, and an exquisitely colored natural setting. Since 1966, the French military has conducted about 175 tests here and on neighboring Fangataufa Atoll. Atmospheric or above-ground tests ended in 1974. The first underground tests were conducted on land, but were moved to the center of the lagoon in 1981 to avoid further damage to the coral. Underneath the lagoon, a deep layer of basalt, about the size of Colorado's Pike's Peak, provides what French officials describe as the perfect container for a nuclear explosion. Three teams of international scientists in 1982, '83, and '87 have failed to find radioactive leakage at this site. Since May 1992, France maintained a self-imposed moratorium on nuclear testing. ''I've eaten the fish, drunk coconut milk from the trees, and swum in the lagoon,'' says Gaston Floss, the president of French Polynesia. ''Do you think I would have done that if there had been the slightest risk?'' Minimizing risk is part of the culture here, says one Foreign Legion officer serving at Mururoa. ''The bars close at 10 p.m., and the road is closely monitored for speeding. We have to convey a sense of safety here.'' Omnipresent signs call on workers here to ''Keep Your Atoll Clean.'' Civilians and military personnel working here earn double what they would in other assignments. Mururoa is the only site where a Foreign Legion officer can serve for less than the usual five-year contract. About 1,500 live here, including 500 civilian employees of the French atomic agency, and 1,000 Air Force, Army, Navy, and French Foreign Legionnaires. About 10 to 15 tons of food is flown in each week, including four tons of fruit and vegetables from Tahiti. Four tons of fish a month is provided by fishermen in local waters. In addition to an industrial zone, there are two waste-processing plants, a radioactive-waste dump, a central kitchen, two outdoor movie theaters, tennis courts, a soccer field, martial-arts training facilities, restaurants, clusters of two-room cottages, and a 15-acre nursery to produce flowers. AT the local PX or commissary, you can pick up ''Mururoa '95'' T-shirt, Foreign Legion cap ash-trays, flowered polyester sport shirts, and Mururoa buttons. When first discovered by an Englishman in 1792, Mururoa was sparsely populated. Cyclones in 1903 and 1906 drove full-time inhabitants off. In the late 1920s, enterprising British and French coconut merchants planted about 35,000 palm trees, which were subsequently harvested about two to three months of the year. When French officials designated Mururoa as their test site, they declared that the site was uninhabited. In drawing up their maps, French officials replaced traditional Polynesian names on the atoll with the French names for flowers and women, such as Camelia, Anemone, and Hortensia. And, in a move more resented by local historians, they misspelled the name of the atoll. It should be Moruroa, from the Polynesian words moru (passage for fish) and roa (long or extended), says Marie-Therese Danielsson. She and other local writers retain the traditional spelling. The sound of the sea crashing against a double sea wall around the outside of the atoll is a constant presence. By 10 p.m., when bars and the movies are closed, the only sound one can hear is a lone radio or a passing car. ''It's a job,'' explains a young Polynesian truck driver. ''The hardest part is living without my family. That and the fact that there aren't any American films. They are mostly all French.'' For Col. Patrice Delcourt, commander of the test site, the greatest problem on Mururoa is the isolation. ''It's human nature to focus only on what's happening here. We need to fight to keep informed about what's happening in the rest of the world.'' For environmental groups and most of Mururoa's Pacific neighbors, the key problem is finding out what's happening on the island. Last week, South Pacific environment ministers meeting in Brisbane, Australia, called on France to accept an independent research program to assess the structural integrity of the atolls and the timing and scale of any leakage of radioactivity. French officials promise more openness in this latest and final round of testing than in any previous. But they also insist that their own presence is proof that their activity is not dangerous. In Fangataufa, 27 miles to the south, they point to the birds. Here, French scientists conducted some of their largest atmospheric and underground nuclear tests, devastating natural life on the atoll. Today, many seabirds are again nesting on the site - frigate birds, gannets, and red tails. No independent studies have yet been conducted on the structure, ecology, and radiation levels at Fangataufa. Even the French scientists have no idea why the birds returned.