Next Step : U.N. Rides High After Cold War : The world body was expected to founder in the new era of detente. But the Security Council’s tough sanctions in response to Iraq’s invasion have left the organization with new prestige and potential.

When President Bush was seeking broad international backing for a sweeping economic and trade embargo against Iraq early last week, he took an unusual step: He turned to the United Nations for help.

He wasn’t disappointed. Much to the surprise of some observers, within hours the U.N. Security Council voted to commit the entire membership to support economic sanctions against Iraq--the most sweeping such penalty that the 159-country organization has imposed since the international boycott of the rebel British colony of Rhodesia in 1967.

Even more surprising, the rest of the United Nations’ broad array of members went along with barely a protest. To many American policy-makers, more used to dismissing the world organization as an impotent “talking shop,” it seemed to be one of the United Nations’ finest hours since it was formed in 1945.

As a result--and to the astonishment even of some officials in its own secretariat--the United Nations is preparing for its 45th annual General Assembly meeting Sept. 18 with more prestige and with more potential to serve as a serious participant in high-level global politics than at any time in recent years.

“The Iraqi embargo incident appears to have given the U.N. a new lease on life,” said Joseph E. Goldberg, professor of political science at the Pentagon-sponsored National Defense University. “For the first time in a long time,” he said, “its future looks good.”

The irony is that the revival comes at a time when the United Nations was expected by many to be foundering in a possibly futile search for some new role in the post-Cold War world.

With the relaxation of East-West tensions and the emergence of new international organizations, such as the Conference on Security and Cooperation in Europe, in more active peacemaking roles, some analysts thought that the United Nations would become increasingly irrelevant.

But as last week’s Security Council action showed, the easing of U.S.-Soviet hostilities may ultimately prove to have unshackled the United Nations, freeing it to play a more serious role not only in mounting international economic pressure, but on other political issues as well.

Indeed, last week’s unanimous vote on the Iraqi sanctions issue provided a textbook example of the way the U.N.’s charter envisioned the organization would operate: The Big Five powers that hold permanent seats on the Security Council--the United States, the Soviet Union, Britain, France and China--would provide overall direction for the organization, which the rest of the membership would carry out.

But the system fell apart almost from the beginning as the U.S.-Soviet rivalry deepened into the Cold War. In almost every conflict since Korea, the Security Council has split along East-West lines, resulting in deadlock or at least paralyzing delays.

“The U.N. can be useful now because the reasons it had not been useful in the past no longer exist,” Goldberg said.

The big question for now is whether the Iraqi sanctions vote was an aberration or the precursor of a new, more substantive role that the United Nations may play in the post-Cold War world. In either case, it may take time before the answer is clear.

Analysts caution that it’s easy to overstate the implications of last week’s Security Council vote. In that case, the issue was clear-cut: emergency reaction to an obvious threat--the prospect that the world could lose its oil supply, strangling the global economy.

Also, the United States and its allies badly needed international cooperation to help make the embargo work. Going it alone simply wasn’t a very realistic option, a U.S. economic strategist conceded. Going to the Security Council was an easy choice.

But how often the great powers will choose to make use of the United Nations in future squabbles will depend on a variety of factors, from the political dynamics of the issue involved to the effectiveness of the new secretary general who will replace Javier Perez de Cuellar upon his anticipated retirement next year.

“It’ll be on a case-by-case basis,” Goldberg predicted.

Brian Urquhart, a Briton who once held the U.N.’s second-ranking post, worries that the organization “may be trading the old East-West split for a North-South division,” which could paralyze the organization in future years as much as U.S.-Soviet quarreling did in the past.

When the United Nations was founded in San Francisco, the then-51 member countries were dominated by the northern industrialized powers. Third World countries were barely represented at all.

Today, however, developing countries hold a clear majority in the General Assembly and often stymie new initiatives that the industrialized powers want to push through. More often, the poor nations push for a larger share of the world economy than the rich are willing to give.

Indeed, the United Nations’ decidedly Third World tilt had been a major factor behind U.S. abandonment of the organization as a serious forum for global problem-solving--particularly within the General Assembly, where developing countries have equal voting weight with the industrialized nations, giving the Third World a majority in any vote.

The estrangement came full circle during the Reagan Administration, when the United States--at a North-South conference in Cancun, Mexico, in 1981--served notice that it no longer would pay attention to the Group of 77, the U.N.’s once-influential Third World caucus.

In recent years, Washington dropped out of the United Nations Educational, Scientific and Cultural Organization, a Third World-run, Paris-based bureaucracy that American investigators found was rife with corruption and anti-Western rhetoric.

The agency since has recanted and launched reform efforts, but neither the United States nor Britain has returned to membership.

Another Third World administered U.N. agency--the Geneva-based United Nations Conference on Trade and Development, or UNCTAD--still is dismissed as a laughingstock by most industrialized countries. That, too, would have to be overhauled in any wider new role, analysts say.

The World Court in The Hague, which is also U.N.-related, has had mixed success. Although the United States has used the court to resolve some issues, such as its freezing of Iranian assets in the late 1970s, it also has disregarded the court when that suited U.S. aims, as when Nicaragua’s Sandinista government won a suit charging Washington with aggression.

One major problem that remains for the United Nations is collecting the money it needs to carry out its far-flung operations.

The United States only recently paid part of about $430 million in back dues that it has allowed to mount up over the last few years. South Africa owes the United Nations $37 million. Iran owes $12 million.

As originally conceived, the United Nations was intended to encompass a network of regional organizations that would form the courts of first resort under a global rule of law. The United Nations itself would deal only with disputes that could not be settled at the regional level. If necessary, it would enforce its decisions with armed forces supplied by member states.

The concept of a permanent U.N. army never got off the ground, however, a victim in part of a nuclear age that added an entirely new dimension to the notion of national security.

The United Nations is still primarily a forum, not a world government. And therein lies its big problem, said Goldberg. “Countries will continue to use it to promote their own national interests,” he said.

Urquhart predicted that the United Nations may now be in for a “heartfelt re-examination” of itself to accommodate the tremendous changes that have occurred in the world since 1945--particularly those in the last 10 months, since the opening up of the East Bloc countries.

He also suggested that the focus of the organization may change to more peace-related issues. “Until now it’s been largely security matters,” Urquhart said. But “the new priorities will be economic development, human rights and preservation of the environment.”

“The U.N.’s one great advantage is that it’s the only truly international organization in existence,” Urquhart said. “But if it’s going to keep going, it will have to work out its new mission.”