Some of them were still in their teens when they first came to work at the United Nations, the high-minded new experiment in peace that was taking shape in temporary headquarters in Lake Success. They had seen war, in some cases firsthand, and resolved to be part of the then-small cadre that thought it could, literally, change the world.

Close to 40 years later, they work in one of the world's great bureaucracies; their desk tops overflow with paper. They hold wordy titles no outsider can remember. They continually read and hear reproaches of the organization to which they've dedicated their working lives. They themselves know very well the limitations of the United Nations.

Yet, as the U.N. marks its 40th anniversary this month, three of its most senior staff members, reflecting on their careers, say that the idealism with which they began -- however sorely tested -- has survived.

Achille Hodak works in a fluorescent-lit office of surpassing barrenness. There's not a poster, photo or calendar hung on his walls, and there's a reason. "You have to ask for somebody to put up a hook; you can't put this here or that there; you need a building manager," he shrugs. "Bureaucracy. It's going to choke the U.N."

At 57 the senior Frenchman at the United Nations, Hodak can wax eloquent on the topic of his employer's legendary penchant for paper shuffling. "The amount of work that has to be repeated so one can check on another," he sighs. "A report, a report, a report. Everybody would be pleased if we could cut out the paper work . . . But," he concludes, "I am lucky."

For one thing, he's climbed through the ranks. Hodak joined the U.N. as a newly arrived immigrant of 18 who happened to meet U.N. Trusteeship Division Director Ralph Bunche's secretary. "She told me the U.N. was looking for people who were bilingual. I had high school English, and every time I wanted to say something I had to spell it out to be understood. I couldn't understand the Americans, either. But I was hired. I started as a messenger in 1946 when the U.N. was in Lake Success. From there I went to Documents . . . someone had to stack them up and pull out the staples." From such admittedly humble beginnings, Hodak rose to become a trade expert and is now chief of International Trade and Transport Statistics.

"We are trying to give every country the tools to develop trade," the chief explains across his printouts. "They need statistical information to know who their competitors are and how they can do better. Countries are reluctant to give certain pieces of information," he adds, with a trace of smugness, "but we have methods of estimating what is said to be confidential."

The resulting series of publications stretches across the chief's bookshelves. "They're huge now, like telephone directories," Hodak says. "The volume of information has increased tremendously since after the war."

The other reason Hodak feels lucky is that he can look back on one lasting achievement. Stationed in Geneva in the '70s, he created a computerized data base that makes trade figures from member countries comparable to one another. "They were convinced of failure," he says of certain nameless colleagues. "They'd been trying for years to develop an integrated data base of trade information. It became a reality in 1980, the only one in the world. It's still utilized. I have been very proud to have participated."

France Vacher was living in Paris when the U.N. began hiring staff. She passed the new organization's typing test and was assigned space on a flight to New York.

"I was hired by mistake, actually, because I was 19, not of age. At the last moment my parents authorized it and I got on the plane," Vacher remembers with amusement.

It was something of a coup; other, older girls from Lyon were miffed that a teen-aged novice was winging off to adventure instead of them. Vacher, now 58, has never gotten over the feeling that she is blessed to be working at the U.N.

"I had seen deportations; I didn't understand how that could happen. I had seen bodies, bombings, horrible things," she shudders. "We didn't have enough to eat. I knew I didn't want to see this ever again."

The U.N. was almost familial then, a troop of idealists housed in a Lake Success factory. "Part of the factory was turning out airplane parts for war," says Vacher, "and our part was working for peace. We knew everyone at the U.N. in those days. Everyone passed through the same corridor." Since then she has worked, primarily as a secretary, in various departments -- Conference Services, Economic Affairs, the World Food Conference. For the past 12 years, she's been a research assistant in the Department of Technical Cooperation for Development. Like many U.N. offices, its function is virtually undecipherable from its title, but Vacher tries to explain.

"I work with a group of economists in the field of planning . . . to help socioeconomic development in the less developed nations, according to their available resources," she says carefully, trying out various combinations of wording. She does not want to say "within the limitations of their available resources" because "we shouldn't have limitations, hmm? Just possibilities."

Though Vacher has spent nearly all her tenure in New York, last spring she went to Katmandu, Nepal, to help with a workshop in financial planning for developing countries. "It was very, very interesting and very fruitful," she says warmly. "I would have liked to go on more missions but it didn't work out so."

She will admit to disappointments -- mild ones -- but not to disillusionment. "So many times I hear people denigrate the U.N.," she worries. "People are pleased to write about its weaknesses. The U.N. is only reflecting whatever we are prepared to offer it." Her lined face glows. She talks about the U.N. Building as "a cathedral."

Gradually it has become the center of her life. She commutes from Queens ("I do need nature") but spends much of her free time in activities spun off from the U.N., like the United Nations Singers and the "Peace Meditation" program. "For the last 15 years we've had meditation sessions under the leadership of Sri Chinmoy," she explains. "It's unofficial, only an association of staff and delegates, about 75 people. We meditate together with our leader twice a week, quiet meditation, to help bring about peaceful feelings. I'm sure it's something that spreads, like waves."

Irene Melup is transcultural: Her Russian parents raised her in Poland and in the United States; she speaks eight languages with varying degrees of proficiency; she has friends around the globe and tends to refer to life outside the U.N. as "the outside world."

She joined the U.N. staff in 1946 soon after graduating from Bryn Mawr College. That is as close as she will come to giving her age. A dramatically graying woman dressed all in black, Melup is not anxious to talk about herself, but she is very anxious to talk about her work.

She is senior social affairs officer in the Crime Prevention and Criminal Justice Branch of the Center for Social Development and Human Affairs of (deep breath) the Department of Economic and Social Affairs. "People don't know the U.N. is involved with crime prevention," she complains. "The attention and the criticism always center on the political dimension. But in the social field, the study of issues, meetings where countries can exchange information, assistance to governments, a lot is done that nobody knows about."

Melup rummages around in cardboard boxes for documentation. "We have five-year congresses, for instance; our Seventh U.N. Congress on the Prevention of Crime and the Treatment of Offenders, in Milan this summer, drew 1,500 persons from 124 countries," including attorneys general, prosecutors, chief justices.

The conference, she suggests, pulling out stacks of mimeographed reports, would really make a much more worthwhile story than her personal memories. "With the increasing transnationalization of crime," she lectures, "with organized crime, drug traffic and terrorism -- these are problems that can't be attacked at the national level."

Melup, who now describes her job with words like "organize," "facilitate" and "provide support," remembers when the path seemed simpler. "It was the great challenge, the great adventure," she says. "When we started, there were no precedents; it was much smaller, almost like a mutual self-help group."

Over the decades she has wrestled with the issue of how effectual the U.N. can be. One can imagine her pressing her arguments at cocktail parties in Asia and U.N. cafeterias in Europe. "In a sense one has no power, but in a way one does have leverage, just by providing information, putting people and institutions in touch with one another," she says. "Whether it's a report that proposes new ideas, that sets governments or institutions thinking, or something concrete like these crime prevention institutes, if one has a worthwhile purpose -- and our purpose is worthwhile -- then it makes a difference."

"It's a very consuming kind of thing, a world in itself," reflects Melup. "Some of us really devote our lives to it." Melup, for example, lives alone in Manhattan and believes she could never have juggled a spouse and children with the nearly round-the-clock demands of her post. "Half the time I pay to go to meetings out of my own pocket," she laughs. "I think I have the distinction of being the only U.N. staff member to be here this long without a savings account.

"It's like a drop in the ocean: The needs are so tremendous and it's so finite what one can do. We are 10 people here in this office, to deal with crime worldwide. God! But things are done."