The Inter-American Development Bank, which quietly has loaned $17 billion from its offices on 17th Street NW over the last 20 years, meets today to reelect Mexican Antonio Ortiz Mena as president. He is unopposed.

After initial U.S. resistance to creation of the bank, successive administrations in Washington have used it increasingly to administer assistance to the area and have encouraged creation of banks on the same model in Asia and Africa.

Under Ortiz Mena, 68 -- who was elected to his first five-year term in 1970 -- the U.S. pre-eminence as the major donor has been diluted by participation of Canada, Israel, Japan and 14 European countries. In all, 42 nations will be voting today.

Bank officials, pointing to the institution's ability to conciliate the region's divergent political tendencies, point to its performance on such controversial issues as lending to revolutionary Nicaragua. Although the United States government triggered volumes of testimony on the merits of lending $75 million -- which has yet to be distributed -- the IDB is providing without fanfare $172 million that began to flow shortly after the 1979 revolution.

Ralph A. Dunga, the U.S. representative, said the bank's most important recent achievement under Ortiz Mena is that "it has focused its lending on the poorest countries and the poorest people."

Concessionary loans to the more affluent Argentina, Mexico and Brazil over the last 10 years came to less than $4 per capita, while the 10 poorest countries received more than $56 per capita, according to bank statistics.