The United States, in a further distancing from New Zealand, is withdrawing its security umbrella from that Pacific country because of its refusal to accept port calls by nuclear-armed U.S. warships, Secretary of State George P. Shultz said today.

"We part as friends but we part company as far as the alliance is concerned," said Shultz to New Zealand Prime Minister David Lange after a 40-minute meeting that tried but failed to resolve deepening differences over the meaning of the 1951 Australia-New Zealand-United States security treaty known as ANZUS.

Today's action goes further than previous U.S. action in announcing that the United States no longer feels bound to provide a security guarantee to New Zealand. The new step was prompted by impending parliamentary action in New Zealand to put into law its ban on nuclear-armed or nuclear-powered ships.

Lange, whose New Zealand Labor Party has taken an unyielding antinuclear position since coming to power in July 1984, predicted the U.S. action would have a "short and spectacular" effect at home.

New Zealanders will ask whether they are now subject to Soviet attack without anyone coming to their defense, Lange said. He suggested the answer is that nothing much has changed, saying that ANZUS was "the ultimate cop-out treaty" because it only called for consultations in case of military threat and did not guarantee protection.

U.S. officials said tonight that no immediate changes in fleet operations are expected because the U.S. Navy will no longer be protecting New Zealand. No Soviet threat is in sight to the thinly populated island nation, the officials said.

"The people of New Zealand are not afraid" without U.S. defense, declared Lange. "They don't see a nuclear weapons defense of New Zealand as a security assurance -- they don't see being defended by nuclear weapons as any sort of assurance."

The refusal of New Zealand to accept U.S. nuclear warships, which rarely call at its ports anyway, has been taken seriously rather than as a petty irritation primarily because the Reagan administration fears that the antinuclear policy could spread unless firmly rebuffed.

In February 1985, following New Zealand's firm refusal to accept a proposed naval port call unless Washington indicated whether the ship was carrying nuclear weapons, nearly all joint exercises, intelligence sharing and other military cooperation was halted by Washington. The United States has long refused to confirm or deny whether its ships carry nuclear weapons.

Shultz, at a press conference to conclude two days of meetings with Southeast Asian and Pacific community states, said New Zealand's nuclear ship ban had withdrawn an "essential element" of its participation in the ANZUS treaty alliance.

"In the light of this, the United States considers that the treaty, at least as it has been understood, doesn't apply in the sense of the responsibility of the United States to extend its security responsibility to New Zealand," Shultz said.

Aides to Shultz declined to specify a timetable for nullifying U.S obligations to New Zealand under the pact. They said they did not believe congressional approval was needed, but expressed caution, saying U.S. security guarantees evidently have never been withdrawn from an ally before.

Philippine Vice President and Foreign Minister Salvador Laurel told reporters he understands that no nuclear weapons can be stored at the two U.S.-leased bases here without Philippine consent, and that no such weapons have been reported.

A U.S. official familiar with such questions said later, however, that the United States has "no agreement" with the Philippines regarding nuclear weapons.