A senior United Nations official predicted Washington would ignore a World Court ruling that said the United States violated a U.N. treaty by trying to close the PLO's New York office.

In an advisory opinion issued Tuesday, the International Court of Justice, as the court is formally known, ordered the United States to submit to arbitration in its dispute with the United Nations over the Palestine Liberation Organization's observer mission to the United Nations.The court is the judicial arm of the United Nations. It has no enforcement powers and depends on voluntary adherence to its rulings.

The Reagan administration's dispute with the U.N. arose from legislation signed into law by the U.S. Congress in December that classifies the PLO as a "terrorist organization" and bars it from operating on American soil.

The U.S. government maintains that the anti-terrorist law takes precedence over any international agreements.

Carl-August Fleischhauer of West Germany, the U.N. undersecretary-general for legal affairs, told reporters after Tuesday's ruling that he doubted the United States would submit to arbitration.

"We want harmonious relations with our host country," Fleischhauer said. "We are ready to go to arbitration. It is now basically for the United States government to decide what conclusions it draws from this ruling."

"It is a pleasure to be proved right," Fleischhauer's boss, U.N. Secretary-General Javier Perez de Cuellar, said of the ruling during a press conference in New York.

Although the court took pains to dodge the question of whether Washington's attempt to close the PLO office is legal, the ruling was seen in Vienna as an implicit condemnation of the U.S. effort.