Hopes Rise for Passage of Permanent Nuclear Treaty : Diplomacy: New security assurances from the acknowledged powers brighten outlook for the pact.

With all five of the world’s acknowledged nuclear powers offering fresh security assurances to the rest of the world, a senior U.S. official said Thursday that the outlook “is increasingly favorable” for permanent renewal of the 25-year-old treaty credited with curbing the spread of nuclear arms.

In a flurry of diplomatic activity Wednesday and Thursday, the United States, Russia, Britain, France and China promised not to use their nuclear arms against any non-nuclear state that abides by the restrictions of the Nuclear Non-Proliferation Treaty. The step is intended to persuade the nuclear have-nots that it is safe to extend the treaty indefinitely.

In a closely related development, the U.N. Security Council prepared to vote next week on a resolution offering diplomatic, medical and humanitarian help to non-nuclear nations that may face nuclear attack. And Britain and France removed an important obstacle to passage of a separate treaty prohibiting nuclear tests.

John Holum, director of the Arms Control and Disarmament Agency, told reporters Thursday that more than 80 countries already have indicated that they will vote for permanent renewal of the treaty during a conference beginning April 17 at the United Nations. It will require 87 votes, a majority of the 173 participating countries, to eliminate the expiration date, although Washington wants far more than that to demonstrate overwhelming approval of the treaty.

“There is strong and growing support,” Holum said.

But, he conceded, “none of those commitments, including public ones, can be considered binding until the vote is taken.”

The Clinton Administration has made permanent extension of the treaty the centerpiece of its effort to prevent the spread of nuclear arms to “rogue states” such as Iran, Iraq, Libya and North Korea.

In many ways, the pact has been the most successful arms control effort in history.

When it took effect in 1970, only five nations had nuclear arms but dozens of others were considered to be candidates. There have been no acknowledged additions to the nuclear club, although Israel, India and Pakistan are widely believed to have established clandestine arsenals and a few other countries, including Iran and North Korea, are believed to be trying to develop nuclear arms.

Holum said at least 40 nations have the technological and economic resources to produce nuclear weapons but almost all of them have refrained from doing so.

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With France adding its declaration on Thursday, all five big nuclear powers have now offered assurances that they will not attack non-nuclear states.

The United States, Russia and Britain had offered similar pledges years ago, but France and China issued the promise for the first time. The assurances are not airtight. They apply only to nations that are complying with the treaty and also seem to contain other loopholes that could allow the use of nuclear arms.

Britain and France also agreed Thursday to drop their insistence that a proposed nuclear test-ban treaty contain a clause permitting testing in exceptional circumstances.

The United States, Russia and China already support a total ban on testing. The nuclear states hope that a comprehensive test ban will persuade a few holdouts to vote to extend the non-proliferation treaty.

U.S. officials expect several additional countries to sign the non-proliferation treaty before the review conference opens.

But Israel, India and Pakistan have made it clear that they will continue to hold out. Israeli and Egyptian negotiators are now trying to work out a dispute over the Jewish state’s position. Cairo had earlier vowed to lead an Arab boycott of the treaty unless Jerusalem signed on, but it has since retracted that threat.