The South Pacific, since World War II a virtual American lake, is becoming a scene of new competition between the United States and the Soviet Union. Gathering resentments over US fishing practices and French and American nuclear policy, combined with a political awakening among leaders in several of the island nations of the South Pacific, have led to a gradual erosion of US influence in the region.
While experts agree that there is little immediate danger to US interests there, many worry that present trends could eventually lead to a political realignment in the South Pacific. Especially of concern in Washington is the prospect of expanded Soviet influence in the area.
``What the Soviets see here is an almost irresistible target of opportunity to penetrate an area where the US has always been able to operate without impediment,'' a State Department official says.
The region, lying north and west of Australia and covering an expanse of ocean twice the size of the continental US, includes nine independent island nations and a number of other territories with ties to former colonial powers.
The region is important to the US because of its proximity to shipping routes to major US trading partners along the western rim of the Pacific. It is also the site of a missile testing range, at Kwajelein in the Marshall Islands, considered key to the development of President Reagan's proposed antiballistic-missile defense system.
Political changes are transforming many of the island nations of the South Pacific. A rising spirit of nationalism has swept across the region, fed by economic discontents, local anticolonial movements, and dissatisfaction with the perceived indifference of the US to those nations' needs.
The focal point for much of this sentiment has been Walter H. Lini, prime minister of the tiny island nation of Vanuatu, whose Melanesian solidarity movement has galvanized regional discontents and created new diplomatic openings for Soviet-bloc allies like Cuba and Vietnam.
To some extent, these developments are seen as part of a natural process of political evolution. A decade after the end of colonial rule, leaders in the region have become more confident and independent.
``Countries like Vanuatu are acting out of frustration for being taken for granted by the US,'' one Pacific expert says.
By far the largest cause of the erosion of goodwill toward the US has been the sensitive issue of fishing rights. Tuna fishing is a vital means of livelihood for many of the islanders. But US tuna boats, which first entered the region in the late 1970s, have refused to pay fishing fees to island governments, while the US government has not recognized claims by the islands to exclusive fishing rights extending 200 miles offshore.
The result has been a setback for US relations with the islands and new diplomatic opportunities for the Soviet Union.
Last year, the island nation of Kiribati became the first Pacific island nation to accept a Soviet offer to pay for the rights islanders claim US fishermen have usurped. The Soviets have agreed to pay Kiribati $1.7 million in return for rights for 16 Soviet trawlers to fish within the 200-mile limit. In the US, the significance of the deal is a matter of disagreement.
``As a result of playing the Soviet card, Kiribati has achieved its goal of greater economic independence,'' says Peter Hays of Nautilus Research, a public-interest group based in Glover, Mass. ``It hasn't provided the Soviets with one iota of political or military advantage.''
But others are more concerned.
``The Soviets are looking for an island state that may someday become what Grenada once was, a staging ground for political mischief and a complement to Soviet strategic interests in the Pacific,'' says Pacific specialist Richard Fisher of the Heritage Foundation.
State Department officials entertain the more subtle fear that if impoverished countries like Kiribati get used to the Soviet fishing subsidy, Soviet threats not to renew the arrangement could be used as a form of blackmail to gain other concessions from the island nations, including shore privileges and possible eventual base rights.
Experts say that for the US to regain lost ground in the Pacific, as a minimum the US tuna industry will have to pay for the right to fish within the territorial limits claimed by the islands. The State Department is negotiating a fisheries agreement with a group of nations in the area. Without such concessions, analysts warn, other countries will follow Kiribati's lead by signing agreements with the Soviets.
Regional experts also urge expanded diplomatic contacts with the Pacific nations. Only two US embassies service the entire Pacific region. More contact would help break down the sense of isolation that has weakened strong historical ties to the US among the islanders.
Finally, some experts say the US may need to take a more active hand in discouraging French nuclear testing off Mururoa Atoll. Resentments in the region run deep over the perceived injustice of endangering local populations to test warheads for possible use in a conflict half a world away.
``If you want the South Pacific to become an area where the Soviet Union, Cuba, and others of that stripe can find fertile ground for anti-US propaganda, then continue with a policy of indifference to what the French are doing there,'' warns F. Rawdon Dalrymple, Australia's ambassador to the US.