A row between France and New Zealand over the sinking of the Greenpeace environmental group's flagship underscores growing antinuclear sentiment that is irritating relations between Pacific island nations and western powers.

In addition to France, the United States is the target of much of the antinuclear feeling, and the Soviet Union appears to be trying to take advantage of it and to establish its own foothold in the region.

France has been condemned repeatedly by Pacific states for conducting nuclear weapons tests in its South Seas territory of French Polynesia. The United States stopped nuclear testing in the Pacific in 1958, but continues to fire unarmed intercontinental missiles at Kwajalein Atoll in the Marshall Islands.

In the latest test, on Aug. 23, an MX missile with six unarmed warheads was launched from Vandenberg Air Force Base in California. It covered more than 4,000 miles before splashing down at the Kwajalein Missile Range, considered one of America's most crucial military facilities. Built up since 1959 at a cost of more than $1 billion, it is one of a number of U.S. bases in the Pacific that Moscow clearly would like to see become a focus of protest activities.

In a recent newsletter distributed by the Soviet Embassy in Bangkok, Moscow warmly praised a treaty approved by the 13-member South Pacific forum last month declaring their region a nuclear-free zone.

The treaty, signed by eight of the forum's member states, was a "major contribution to easing military confrontation in the world," but Washington was hostile to it, the Novosti press agency article charged. It accused the United States of "forcing upon the small states in the Pacific the deployment of U.S. nuclear weapons" in an effort to "turn that area into an American forward nuclear-missile position."

The Soviet article said the treaty also "highlights the incompatibility of French nuclear tests with the security" of the South Pacific states.

The Soviets also have repeatedly applauded New Zealand's decision to ban port visits by nuclear warships, a ban that Washington regards as inimical to the 1951 ANZUS defense treaty linking Australia, New Zealand and the United States.

Signed in Rarotonga in the Cook Islands Aug. 6, the nuclear-free zone treaty bans the manufacture, stationing or testing of nuclear weapons in the region, but allows the transit of nuclear-powered or nuclear-armed ships and leaves port visits up to individual countries.

The signatories include Australia, New Zealand, Western Samoa, Tuvalu, Niue, Fiji, the Cook Islands and Kiribati. Four states -- Papua New Guinea, Tonga, Nauru and the Solomon Islands -- endorsed the treaty; another, Vanuatu, objected that it was not strong enough.

Not a party to the pact is French Polynesia, where France has carried out more than 100 nuclear weapons tests on Mururoa Atoll since 1966.

The Greenpeace flagship, the Rainbow Warrior, had been preparing to sail to Mururoa Atoll to protest and monitor the latest French nuclear test when it was sunk in New Zealand's Auckland harbor by explosives attached to its hull. One crew member, a Portuguese-born Dutch photographer, was killed.

Two agents of the French intelligence service who had posed as a Swiss couple are awaiting trial in Auckland in connection with the sabotage. At least four other agents who escaped to France -- including three combat frogmen and a woman Army officer -- are being sought for questioning by New Zealand detectives in Paris.

An official French report denied that France was responsible for the sinking, a finding that New Zealand's prime minister, David Lange, ridiculed as "so transparent it could not be called a whitewash."

New Zealand and Australia led a campaign that prompted France to end atmospheric tests in 1975 and move them underground. Since then, France has rejected complaints from Pacific states that the tests -- carried out inside a dormant volcano -- may be cracking the atoll's coral base and could allow radioactive matter to leak into the ocean.

Antinuclear activists and leaders of an independence movement on the French Polynesian island of Tahiti also have charged that the years of atmospheric testing caused an increase in leukemia, thyroid tumors and other cancers.

Similar charges have been leveled against the United States by some residents of the Marshall Islands, a U.S.-administered United Nations trust territory in Micronesia where the American military conducted atmospheric nuclear tests in the 1940s and '50s. One such blast, on Bikini Atoll in 1954, ranks as the biggest American nuclear test in history.

According to Jonathan Weisgall, a Washington lawyer who represents the people of Bikini Atoll, the 1954 test produced more than twice the explosive power expected and contaminated several hundred Marshall Islanders and a Japanese fishing crew with radioactive fallout.

Today, residents of the Marshall Islands, whose total population is about 20,000, have claims of more than $5 billion pending against the U.S. government.

As part of a proposed "compact of free association" with the Marshall Islands, the U.S. government has offered a $150 million trust fund to compensate about 3,000 residents of four atolls directly affected by the tests. By comparison, a $180 million trust fund is being shared by as many as 200,000 U.S. Vietnam War veterans who claim to have been harmed by the chemical defoliant Agent Orange.

The compact would also guarantee American use of the Kwajalein Missile Range for 30 years. A similar compact with the island group of Palau in the Western Carolines has been held up by efforts to resolve a potential conflict with Palau's antinuclear constitution.

During a visit to Papua New Guinea last week, U.S. Assistant Secretary of State Paul D. Wolfowitz told reporters that Washington had "a lot of sympathy" for nuclear anxieties in the Pacific. He acknowledged that U.S. atmospheric tests in the 1950s, "when we did not really realize yet what such tests could do," had "caused a lot of concerns in the region."

Apart from nuclear issues, other concerns that have helped alienate Pacific states include incursions by American fishing boats.

Last month, Kiribati, the former British colony of the Gilbert Islands, signed an agreement giving the Soviet Union the right to fish in its 2-million-square-mile "exclusive economic zone" for a year in exchange for $1.75 million. Kiribati's president, Ieremai Tabai, has been quoted as saying he sought the accord in part because the American Tunaboat Association, which has a powerful lobby in Washington, refused to recognize the zone and fished in it without permission.

Although the Kiribati government has ruled out port rights for the Soviets, western diplomats based in the Pacific see Moscow's pursuit of the fishing agreement as part of a long-term Soviet effort to gain a foothold in a region long dominated by western powers.