United Nations, N.Y. — Like a noisy, disruptive household that suddenly realizes its excesses are upsetting the neighborhood, the United Nations is trying to put its house in order.
Some of the reforming zeal comes with a change at the head of the household. The new Secretary-General, Javier Perez de Cuellar, is acutely aware that the UN is in trouble and in need of repair. He has set the place buzzing by sounding alarm bells and trying to shake the world body out of its apathy and bureaucratic inertia.
At the same time, the rest of the United Nations family seems to be getting the message that unless it gets its act together, there will be even further erosion of the UN's credibility.
The days of what many Westerners viewed as wild-eyed radicalism may not yet have passed at the UN. But they could be waning if the last General Assembly session, which ended Dec. 21, is any guide.
Western diplomats who came braced for a bruising battle this session with the developing countries over such perennial tough issues as racism and economic inequities between the ''have'' and ''have not'' countries were pleasantly surprised.
The issues have not changed. But far fewer third-world countries have been breathing fire at the West, and at the United States in particular. Instead, to many diplomats' surprise, the third-world countries are showing what they welcome as signs of moderation and realism.
An important West European ambassador, as well as a top official in the UN Secretariat, both drew attention to the patience, statesmanship, and cooperation of the African bloc over efforts of the Western ''contact group'' to wrest Namibian independence from South Africa.
On East-West nuclear disarmament, the nonaligned received wide praise for refusing to take sides.
The new, more pragmatic and conciliatory mood is partly the result of a realization that, given the serious state of the world economy, it is unreasonable and pointless to push the recession-hit Western countries too far. Some once-poor nations have grown richer, too, and gained a stake in the Western economic system. Meanwhile, as the world's new nations have become accustomed to their independence, their revolutionary rhetoric has cooled somewhat - and many have become disenchanted both with Soviet actions in Afghanistan and Poland and with the shortcomings of radical socialist economics.
In the UN itself there is also a growing awareness that it is becoming counterproductive to push for resolutions that raise the UN temperature without resolving any problems. And the tougher stance taken by the Reagan administration, hitting back at the failings of its critics, has probably prompted some added caution.
To Jeane Kirkpatrick, the United States ambassador to the UN, who has been a sharp critic of radical third-world tactics at the UN, a ''silent majority'' is now emerging within the developing countries. This has led to more moderate third-world countries splitting away from the radicals.
The result has been a significant shift in voting patterns, which refutes a commonly held thesis in the American camp that the UN with its built-in third-world majority compulsively votes against Washington and therefore delivers propaganda victories to Moscow.
During this past session the General Assembly passed a number of key resolutions that could be interpreted as highly favorable to American foreign policy:
* Afghanistan. A resolution condemning the Soviet occupation and calling for the withdrawal of Soviet troops triumphed by more than 100 votes. As many as 63 nonaligned countries sided with the majority.
Afghanistan is proving to be almost as much a political embarrassment at the UN to the Soviets as Vietnam was to the United States.
Norwegian Ambassador Tom Eric Vraalsen says of the UN vote on Afghanistan: ''It bothers the Soviets tremendously as an expression of public opinion.''
* Kampuchea. Another bid to give Kampuchea's UN seat to the pro-Vietnamese regime in Phnom Penh was defeated by the largest margin yet. The former Pol Pot regime, now fighting a guerrilla war from the periphery of the country, hung onto the UN seat by 90 votes to 29 with 26 abstentions.
* Puerto Rico. A perennial attempt by Cuba and its allies to have Puerto Rico declared an American colony rather than a legal territory went down to its worst defeat ever by 70 votes to 30 votes with 43 abstentions during the recent General Assembly session after vigorous American lobbying. Abstentions came from such key nations as India, Kenya, Mexico, and Yugoslavia. Even at the committee level, the proposal failed to gain the support of the majority of the 25 nations on the Special Committee on Decolonization.
* Israel. An Iranian-inspired move to expel Israel from the General Assembly garnered only nine affirmative votes, despite the opprobrium in which Israel is held at the UN. The US had threatened to pull out of the UN had the vote succeeded.
All these resolutions surfaced in the 157-member General Assembly, where the level of invective has been lower than for some time.
Although the improvement in atmospherics is marked and welcomed, diplomats see little cause for rejoicing. During the past year, they say, the UN chalked up few if any major positive achievements.
The UN Security Council - which has some real decisionmaking powers as distinct from the General Assembly, which is essentially a debating forum - was unable to halt three wars that raged during the course of the year. These were the Argentine invasion of Britain's Falkland Islands, the three-year-old border war between Iran and Iraq, and Israel's invasion of Lebanon. Instead, the failure to resolve these conflicts brought another dip in the UN's credibility worldwide.
Even in its own backyard, patience with the UN is wearing thin. New York cab drivers, as a protest against UN condemnations of Israel, will often look the other way when they are hailed by people they suspect are UN diplomats. The mayor of New York City, Ed Koch, a critic of the UN, has withdrawn police protection for missions to the UN, ostensibly on financial grounds. Attacks in the US news media on alleged UN incompetence, bias, and fiscal mismanagement are rising in shrillness and intensity.
Meanwhile, criticism of the UN is also mounting inside the organization. Staff morale is described by some officials as at an all-time low. Some 1,500 personnel showed their displeasure recently by briefly walking off their jobs.
A powerful triumvirate - the United States, Britain, and the Soviet Union, three of the five veto-wielding permanent members of the UN Security Council - have served notice on the Secretary-General they want a lid put on ever-rising UN expenditures.
Although UN expenditures have risen sharply in recent years, some diplomats see this less as a serious economic threat than a gesture of growing irritation since the respective amounts paid by the protesting governments are not that large - at least in terms of their other expenditures. The US, for instance, while admittedly the largest single contributor to the UN system, is actually ranked below Lesotho, Botswana, and Togo when contributions are figured as a percentage of the gross national product.
Responding to problems such as these and the sharp dip in the UN's popularity , Secretary-General Perez de Cuellar gave a remarkably frank documentation of the UN's shortcomings in his annual report this past fall. His assessment and his calls for reform have had the UN buzzing ever since.
Delegates have responded with an ''it's too soon to judge'' caution. Yet there is a consensus that Mr. Perez de Cuellar not only has got off to a promising start, but also has several things going for him that provide him with a solid foundation on which to build.
1. As a former ambassador of Peru who has served in Moscow and as a former high-level UN emissary, he is a known quantity to the major powers on whose good graces his political survival depends.
2. His third-world credentials are impeccable. As a result, he does not feel obliged to woo the third world by indulging in empty condemnations of South Africa and Israel.
3. He was drafted for the office and therefore has no political debts. He insists he will not seek re-election when his five-year term runs out in 1987.
4. Unlike his tall, dapper predecessor, Kurt Waldheim, who is chided for being too preoccupied with his own reputation and too hesitant to rock the political boat, Perez de Cuellar is seen as a man of greater boldness, political conviction, and intellectual breadth. As an indication that he may be determined to be his own man, Mr. Perez de Cuellar, over the protests of the Warsaw government, decided to hold an inquiry into human rights in Poland.
So far, the new Secretary-General is also proving more innovative. He favors preventative diplomacy. He wants to get members of the Security Council and the parties to a dispute together and to have them break up into working groups even before controversies become military conflicts.
In the past the UN has been attacked either for not getting involved in international crises, like the Nigerian civil war in the 1960s, or for getting its feet wet too late to make any difference.
To counter this kind of criticism the Secretary-General is already working quietly on the Namibian issue and the Guyana/Venezuela border dispute. He also intends to send out inquiry teams, a sort of diplomatic radar scanning that will enable the Secretary-General to spot potential trouble spots quickly.
Although there is some skepticism just how far the Secretary- General can move on his own, his activism is being widely endorsed. He came to the Falkland crisis late and only after the then Secretary of State Alexander M. Haig Jr. was unable to make any further headway. Yet unobtrusively Mr. Perez de Cuellar was waiting in the wings, ready to launch onto center stage when he was needed.
The fact that he didn't pull it off as the prime negotiator in the latter stages of the dispute is seen as no reflection on Mr. Perez de Cuellar's ability.
''Diplomatically, as far as the UN was concerned, it was a success,'' says Guenther Van Well, the West German ambassador to the UN. ''The two parties to the dispute [Argentina and Britain] were willing to agree to his plan. He did a very good job. The plan came to nought because the negotiators couldn't sell it at home to the public.''
Several diplomats said that with adroit diplomacy a skillful secretary-general could accomplish much more for the UN than was generally recognized. Mr. Perez de Cuellar may have to demonstrate just such a skill if the UN is to reverse a popular perception that on the great issues of the day it can be easily bypassed. But at least the political climate in which he works here seems to be a little less stormy.
Next: The UN's shortcomings