New Zealand is determined to keep U.S. nuclear vessels out of its waters but insists that the policy is no threat to its relations with the United States, Labor Party official Helen Clark said yesterday.

Speaking at a news conference as part of a two-week U.S. tour, Clark reiterated the new Labor government's pledge that no nuclear-powered or nuclear weapons-carrying ship or airplane will be permitted in New Zealand territory.

Secretary of State George P. Shultz has said the position threatens ANZUS, the Australia-New Zealand-United States mutual defense treaty of 1951 and that visits to New Zealand by U.S. nuclear-powered vessels are "essential to the continuing effectiveness" of the alliance.

Clark stressed that New Zealand has no intention of leaving the alliance but planned to "review" it in order to adopt "a non-negotiable non-nuclear" position that still gives New Zealand equal decision-making weight with the other members.

"There is no hint in this policy of hostility to the United States," said Clark, who heads the New Zealand parliament's committee on foreign affairs.

"We seek to maintain our role in the ANZUS alliance in a conventional sense."

She said that Spain, Norway and Denmark oppose nuclear weapons on their territory while maintaining military alliances with the United States and that New Zealand had barred nuclear-powered vessels during the last Labor government from 1972 through 1975.

"This is not a whim or fantasy that has suddenly come upon us, but a longstanding policy," she said.

New Zealand's position goes a step beyond that of several nations, including Japan, Spain, Norway and Denmark, which formally ban nuclear weapons but permit or take no position on visits from nuclear-powered ships.

William Lenkerding, spokesman for the State Department bureau of East Asian and Pacific affairs, said that official U.S. policy prohibits confirmation or denial of whether any vessel carries nuclear weapons and that U.S. allies do not ask whether such weapons are aboard visiting ships. All the allies, however, permit nuclear-powered ships to enter.

"We are not excluded from allied countries' waters," he said. "New Zealand would be the first."

Officials worry that if other nations follow New Zealand's lead, it could unravel treaty and strategic arrangements worldwide.

No nuclear-powered vessel has challenged New Zealand's ban since the Labor government took office last July.

But the proposed 1985 list of U.S. ship visits is expected to include some nuclear-powered vessels when it is submitted, possibly this week, and will be rejected if it does, Clark said.