Top officials of the United Nations' controversial education, science, and culture organization are facing some hard choices. These UNESCO officials are resigned to a United States withdrawal - and hence the loss of a major chunk of its income.
But they are only now coming to grips with what programs to chop or economies to make in order to balance their truncated budget. And by far UNESCO's biggest expense is the salaries paid right here in Paris.
A huge 80 percent of the total budget of UNESCO is spent at its be-flagged, glass and steel Paris headquarters. According to the US State Department, other such international and national agencies spend much less on their bureaucracies.
The comparable ratio is 20 percent for the UN Development Program (UNDP). The United Nations Children's Fund (UNICEF) spends 12 percent of its total budget at its New York and Geneva headquarters. For the US Agency for International Development, the figure is 8 percent, and the US Information Agency, 10 percent. (UNICEF, which seeks to improve the health care, nutrition, and general welfare of children, is praised by President Reagan for its ''humanitarian program.'' It is quite separate from UNESCO.)
Such alleged inefficiency is one main reason given for the Reagan administration's decision, announced a year ago and expected to be finally confirmed any day now, to pull out of the Paris-based organization. The other main US charge is that UNESCO has become unduly politicized, backing liberation groups such as the Palestine Liberation Organization and attacking press freedoms.
UNESCO officials vehemently deny the charges. And many American allies who agree that reforms are needed disagree with Washington's decision to withdraw.
But President Reagan is expected to announce the decision soon. In Washington , Gregory J. Newell, OK assistant secretary of state for international organization affairs, notes: ''There is a final recommendation over at the White House.''
The Reagan administration has been under considerable pressure to delay its withdrawal for a year to see if needed ''reforms'' can be accomplished.
Maarten Mourik, the Netherlands' ambassador to UNESCO, wishes the United States would stay another year. ''It is imperative for the reform process,'' he says.
But Mr. Newell says the US ''has never seriously considered'' a one-year postponement of its departure. He argues that US withdrawal will do more to speed up reforms than staying and cites the 1977 US exit from the International Labor Organization in Geneva. ''Change seemed to be possible after we left,'' he said.
After being out of the ILO for three years, the US took up membership again in 1980. Mr. Newell says the US will rejoin UNESCO ''if it returns to its original purpose.''
Charles Hummel, the Swiss ambassador to UNESCO, hopes that UNESCO's desire to have the US rejoin, together with the announcement by the United Kingdom last month that it will leave at the end of 1985, ''will produce real reforms.''
Since the two nations together provide about one-third of national contributions (25 percent from the US, 8 percent from Britain), UNESCO will be forced to concentrate its programs, he says. National contributions make up 63 percent of the UNESCO budget. One complaint of Western industrial nations is that too many UNESCO programs duplicate each other to some degree.
The US helped set up UNESCO in 1945. Its original purpose was to advance the objectives of international peace and the common welfare of mankind through education, science, and culture. Today it has 161 members and a 1984-85 budget of more than $600 million.
Besides paying for headquarters expenses, the money has enabled UNESCO to be involved in campaigns that have brought literacy to more than 15 million adults and young people not enrolled in schools. It has aided in efforts to safeguard ancient monuments and sites - such as Venice, the Acropolis, the Plaza Vieja in Havana, the island of Goree in Senegal, and Sri Lanka's ''Cultural Triangle.''
The organization helps finance hundreds of conferences annually by natural scientists and social scientists. It assists various international scientific programs, such as the International Hydrological Program, the International Geological Cooperation Program, and the Program on Man and the Biosphere.
The United States contribution to UNESCO for the current two-year fiscal period is $86.2 million.
With the imminent US exit, UNESCO faces something of a budget crisis. There is talk of a special meeting of its executive board next month. Officials from Paris were in Geneva last month to discuss how the ILO managed without American money for three years.
Mr. Newell says that next year the United States will channel its UNESCO contributions to other organizations that help in the educational, scientific, and cultural development of third-world nations. These include the United Nations Development Program and two State Department affiliates, the Agency for International Development (AID) and the United States Information Agency (USIA).
Newell claims the shift will mean more money actually being spent on development rather than on salaries and other bureaucratic costs.
A report released Nov. 30 by the US General Accounting Office makes numerous suggestions as to how the management of UNESCO can be improved. It, for instance , found a need for more effective oversight of the general director and secretariat by the governing bodies. And it held that UNESCO has no effective system for evaluating the effectiveness of its program activities, and no adequate means for avoiding unnecessary duplication among its programs.
Despite Newell's arguments that the US departure from UNESCO will not do much damage to national interests, there remains some skepticism, particularly in the science community.
For example, Walter Rosenblith, foreign secretary of the National Academy of Sciences, said, ''In the sciences there is no overall substitute for UNESCO for the time being.'' He said the alternatives mentioned by Newell - UNDP, AID, USIA - lack experience, competence, and inter-institutional arrangements in science. Nor do they have adequate ties with the International Conference of Scientific Unions, an independent body that has received around one-quarter of its finances from UNESCO.
''It is a lot easier to break dishes than to put together a new amphora,'' he said.
But Dr. Frederick Seitz, president emeritus of Rockefeller University in New York and a member of a UNESCO ''monitoring committee'' advising the State Department, says that if the US funnels sufficient money into the International Conference of Scientific Unions and other international scientific organizations , departure ''would not be a disaster. United States science is sufficiently strong that there is a great need to have us in the international scientific family, within or without UNESCO.''
Besides its charge of mismanagement, the United States complains that UNESCO has become involved in political issues beyond the scope of its constitution (such as giving money to liberation groups), introduced statist concepts emphasizing the rights of states rather than individuals into some of its programs (including support for a system of licensing journalists under the guise of protecting them), and allowed its budget to grow unrestrainedly.
Though admitting a need for some management improvements, director general Amadou Mahtar M'Bow denies all of these other charges.
UNESCO officials say headquarters expense comparisons are unfair, since they include some purchases for programs in developing countries and that local costs are often provided by host governments. But several UN experts maintain that UNESCO has the most bloated bureaucracy of any UN agency.