All the weaknesses of the United Nations as an organization were displayed last week--though not intentionally--at what was called a "journalists' encounter" held in conjunction with the second special session on disarmament of the General Assembly.

In the organization's aging but still splendid headquarters building, around one of its familiar conference tables, there were the diplomatic pettiness, the Soviet-vs.-United States backbiting, the Third World holier- than-thou statements, and some old- fashioned, unworkable world government idealism. But those were, relatively speaking, the high points.

Most of the time it was pure, modern U.N. talk--repetitious, irrelevant, inaccurate, basically uninformative. In short, like many U.N. efforts, from peacekeeping to problem-solving, promise far outran performance.

The original description of the "encounter"--when I was first approached about it--was of a series of background meetings with experts set up for a panel of journalists, one from each country, who specialize in defense or disarmament matters. The attraction for me was not only the two days of exposure to arms experts from outside the United States, but also a chance to talk with journalists who write on such matters from the communist bloc.

For the U.N. public affairs department, which promoted the sessions, it was something much different. "The purpose of this encounter," according to a press release handed out to participants, "is to assist mass-media leaders in their efforts to inform the public about the activities of the United Nations in the field of disarmament and to generate support for the goals established by the special Assembly sessions devoted to this subject."

I should have been alerted to the U.N.'s rather proprietary approach to how we journalists were to get aboard the U.N. disarmament bandwagon by the fact that the organization of- fered to pay my transportation between Washington and New York and give me $98 a day per diem-- something that Washington Post rules prohibit but which I learned almost all the other participants, who came from around the world, accepted. 5 When the session was called to order, the chairs of the Soviet, Polish, East German and Mongolian journalists were empty. Later I learned the four, although invited to this country by the U.N., had been denied entry visas by the State Department, victims of the policy to prevent the U.N. disarmament session from becoming an orgy of anti-U.S. public meetings. Needless to say, a Soviet official mentioned the visa denials several times during the sessions in attacking what he once termed "the so-called freedom of the press" in America.

The shallowness of the "expert" presentations became evident with the first substantive speaker, Viacheslav A. Ustinov, a Soviet foreign ministry official who since last year has been undersecretary general of the U.N. for political and Security Council affairs. He droned on with a recitation of past and present disarmament treaties and why the U.N. role, which has been minimal up to now, should be increased. The only note I made was Ustinov's closing acknowledgment that the "possibilities of the U.N. are limited . . . not just in dealing with disarmament but in conventional wars."

After he concluded, one of the journalists asked for a copy of his talk, and the U.N. moderator, who had termed the statement "very useful," then said that we should carry on "off the record" since that "encourages frankness of discussion."

That led a delegate from French- speaking Africa to complain that most of the documents passed around were in English and this bias should be corrected.

A briefing from the head of the U.N.'s Centre for Disarmament, carried with it the perfect U.N. fact--"an important dialogue" on disarmament is going on because the organization's meetings on the subject were up 110 percent last year and disarmament document production grew 160 percent. "Expert studies" by the U.N. were booming. The problem, as can readily be seen by anyone who picks up one of these, is that they depend primarily on material published by other organizations and the press. In short, they are what we term "cut and paste" jobs, and the only thing "new" about them is that they are being turned out on U.N. paper.

A discussion billed as being on problems and obstacles to disarmament turned into presentations by: a Soviet disarmament specialist from Geneva, on his country's position; an Indian representative to the Geneva disarmament conference on his view that the two superpowers and the arms lobbies don't want to quit building weapons; and an American U.N. ambassador attacking both positions, essentially with one-liners.

Three discussions are worth noting for what they illustrate about the U.N.'s disarmament role.

After years of talk, work is now going on in the U.N. commission in Geneva to develop a treaty that would ban radiological weapons. You must understand, however, that nuclear weapons are not to be included and that, therefore, there are at present no weapons that qualify under this category.

After much praise for the Treaty of Tlateloco, which created a nuclear-free zone in Latin America, a Brazilian journalist asked a Mexican ambassador who was speaking as an expert on the treaty why the British had not been condemned and brought to the world court for violating the pact by using their nuclear-powered submarines against Argentina.It took 15 minutes for the Mexican diplomat, in his answer, to get around to saying that Argentina had not ratified the treaty and thus its territorial waters were not covered. And even if they were, he finally noted, the treaty specifically made allowance for nuclear propulsion.

Nonetheless, the Mexican would only conclude that "technically speaking, there has not been a violation" by the British, thus keeping firm his ties of support for the Buenos Aires government.

Finally, there was the presentation of an expert committee's report to the secretary general on disarmament and development. It did not come as much of a shock that the experts found that money spent on weapons cut back the amounts that could be spent on development. What was a surprise, however, was the report's recommendation: that a new subcommittee be set up under the General Assembly's first committee on security matters to study the expert report and make recommendations about its findings and recommendations.

The thing about the U.N., as illustrated by this "encounter," is that the meeting is the message, that style is more important than substance, and that if at first, or second, or at third, or forever, you don't succeed, don't worry. There will be more money and always U.N. people who will be happy to travel anywhere, if someone else pays, to try, try again.