Argentina's Dante Caputo, the new General Assembly president, wasted no time in telling the 159-nation body it must close the economic gulf between rich and poor nations.

As the Argentine foreign minister took the gavel after his election Tuesday, he noted "the remarkable difference between all the progress made toward ensuring world peace and the little or nothing we have done to prevent the widening of the gap between rich countries and a large part of the developing world."Caputo, a 47-year-old former political science professor, defeated the only other candidate for the presidency of the 159-member General Assembly, Barbados' U.N. Ambassador Dame Nita Barrow, by 91-66, with one abstention during a single secret ballot.

The election, the first order of business in the assembly's 43rd session, was portrayed as a showdown between Britain, which backed Barrow, and Argentina, its defeated foe in the 1982 Falklands War.

Caputo won the presidency with strong support from the Soviet bloc, the developing world, Japan, and the non-aligned movement, including India and Pakistan, said diplomats and observers.

Barrow also was backed by the Caribbean nations and numerous Commonwealth countries. The United States was believed to have voted for her, said observers.

Although the presidency is largely ceremonial, it has the power to set the tone of debate. Caputo took advantage of that provision in his opening speech, in which he said the world body has been remiss in redressing economic imbalances.

"One of the clearest examples of this impotence is probably the question of the external (foreign) debt of the developing countries," he said.

"These very high interest rates, together with the pitiless system of successive refinancing plans and the perverse outflow of financial resources of the indebted countries to the creditors, will end up eliminating

the possibilities of investment for the developing world," he said.