Greece's Socialist government has refused the United States permission to modernize nuclear weapons installations here dating back to the late 1950s, Prime Minister Andreas Papandreou has revealed.

Papandreou, who has promoted the denuclearization of Greece and the entire Balkan region since coming to power on an anti-American platform in 1981, disclosed the refusal to Greek journalists yesterday on his return from a six-nation, antinuclear peace conference in New Delhi.

"We refused permission for the simple reason that we aren't playing games. If we are saying to the Greek people that the nuclear weapons will go, we can't be saying to the Americans, 'Go ahead and modernize your installations,' " the prime minister said.

Papandreou said Greece had rejected a request for the updating "of the areas where the weapons are stored." At the same time he made clear that Athens would also reject any application to replace the existing weapons, which he called "obsolete," with others of a more modern type, but he did not say whether the United States had made any such request.

Officials of the U.S. Embassy in Athens said today that they could not comment "on anything having to do with nuclear weapons."

State Department officials in Washington also declined comment, saying they had not seen an official transcript of Papandreou's remarks.

But according to well-informed sources here, there is concern in Washington over the refusal by Greece since 1981 to grant requests for the renovation of nuclear installations, believed to have been carried out routinely under previous conservative administrations in Athens.

According to the sources, the requests involved both maintenance work and construction to improve safety conditions on nuclear weapons sites. There is fear that prolonged neglect could detract from the usefulness of the stored weapons, the sources said.

Nuclear arms were first introduced into Greece under a secret 1959 agreement, and details regarding the kind of weapons involved and where they are remain classified. But the Greek nuclear installations are said by military sources to include "outmoded but usable" Honest John short-range surface-to-surface missiles, nuclear artillery shells and nuclear deep-sea and land mines.

While in New Delhi, Papandreou also said that his government has informed the United States that it will proceed unilaterally to remove American nuclear weapons from Greece, irrespective of the fate of the Greek initiative to create a nuclear-free zone in the Balkans. U.S. officials here would not confirm the prime minister's account.

A meeting to launch the nuclear-free initiative held in Athens last February was attended by Greece, Bulgaria, Romania, Yugoslavia and Turkey. But a follow-up conference in Bucharest is being held up by Turkish objections. Ankara wants the meeting to focus on general issues of Balkan cooperation instead of the proposed nuclear-free zone, according to Turkish diplomats.