A decision by the Reagan administration to not pay a United Nations assessment of as much as $1 million has created a serious challenge to the international body, according to many officials here.
Last week, the United States refused to pay a sum roughly equivalent to its share of the costs of a seabed mining commission being set up under the new Law of the Sea treaty.
The Reagan administration - which opposes the treaty mainly because of a provision which it sees as hindering private mining of seabed minerals - contends that the new seabed commission is not part of the UN.
''The Law of the Sea Preparatory Commission is not a subsidiary of the United Nations and is not answerable to the United Nations,'' says a senior US official. ''Membership in the UN does not obligate a member state to finance any other organization. It is an improper assessment within the meaning of the UN charter and it is adverse to the interests of the United States.''
In the last few weeks, however, the treaty has been signed by more than 100 other countries. And critics of the US decision point out that there is only one precedent for withholding funds from the UN for operations that a particular member state disapproves of: the refusal of France and the Soviet Union in 1960 to pay for the UN Congo peace operation.
Under Article 19 of the UN Charter, a member state that does not pay its contribution can lose its right to vote in the General Assembly. But in 1960 the UN did not challenge the USSR; and France made a separate payment under a different guise to make up for the money it had withheld for the Congo operation.
Theoretically, the UN could challenge the US decision and take its case to the International Court in The Hague. There is little likelihood, however, of UN Secretary-General Javier Perez de Cuellar choosing to cite the Reagan administration.
Some Western diplomats are concerned that, besides creating an added precedent for withholding UN contributions, the Reagan administration gives the appearance of wishing to undermine the UN as a whole. They regret that Washington, by such a decision, seems content to apply to the UN the same sort of big-power standards more frequently used by the Soviet Union.
''The UN is an attempt to civilize international relations. If a country, large or small, decides to go it alone we will quickly return to the law of the jungle,'' says one Western ambassador.
''The US initiative does not and cannot undo the Law of the Sea Treaty which is already becoming Customary Law. It can simply punish the UN for having adopted it,'' says a high Western official.
Estimated withholding of funds by UN member states (to Dec. 31, 1982 in thousands of US dollars) Country Funds withheld from:
1960 Congo Mideast Technical Other Total operation n1 peacekeeping assistance budget forces programs n3 items Albania 47.0 32.9 -- -- 79.9 Algeria -- 142.1 -- -- 142.1 Benin -- 15.9 -- -- 15.9 Bulgaria 273.1 223.0 253.8 49.0 798.9 China 3,988.9 -- -- 114.2 4,103.1 Cuba -- 140.3 -- -- 140.3 Czechoslovakia 1,542.5 5,722.7 -- 216.9 7,482.1 East Germany 1,046.2 9,971.8 1,391.8 147.8 12,557.6 France [4,357.1] n2 -- -- -- 4,357.1 Hungary 791.5 421.4 -- 249.1 1,462.0 Iraq -- 227.5 -- -- 227.5 Kampuchea -- -- -- 70.6 70.6 Laos -- 6.1 -- -- 6.1 Libya -- 441.1 -- -- 441.1 Mongolia 47.0 21.4 -- -- 441.1 North Yemen -- 9.4 -- -- 9.4 Poland 2,272.8 8,254.6 -- 284.0 10,811.4 Portugal 49.7 -- -- -- 49.7 Romania 509.5 -- -- 376.2 885.7 South Africa 814.5 5,403.3 -- 15,895.7 n4 22,113.5 South Yemen -- 10.6 -- -- 10.6 Syria -- 60.7 -- -- 60.7 USSR 25,949.7 119,332.2 18,479.5 5,054.6 168,816.0 United States -- -- -- 612.6 n5 612.6 Vietnam -- 48.7 -- - 48.7 TOTAL 41,689.5 150,485.7 20,125.1 23,077.9 235,378.2
n1 Funds owed since 1960 for the Congo operation. Nations that did not pay refused to finance the operation.
n2 France refused to fund the Congo operation, but paid under a different guise.
n3 Money paid to the UN in nonconvertible currencies (rubles, communist currencies) instead of dollars.
n4 South Africa's withholding of funds is the result of its explusion from the General Assembly.
n5 The US figure is the amount the US owes, but refuses to pay, for a SWAPO office in New York. Source: United Nations