Secretary of State George P. Shultz discussed economic issues with Latin American foreign ministers here today, on the eve of a General Assembly of the Organization of American States that has been overshadowed by tension between the United States and Nicaragua over the issue of Soviet arms supplies.

At a session prior to the opening of the OAS meeting here Monday, officials from 31 countries avoided the sensitive question of Central America, instead devoting two hours to discussing Latin American foreign debt and other economic and trade issues, officials said.

Shultz, who arrived last night for a two-day visit, is expected to discuss U.S. concerns about Nicaragua's military buildup in meetings Monday with ministers from four Central American countries as well as those of Mexico and Colombia. Shultz is also scheduled to address the OAS Assembly.

Asked about a report in The New York Times today that the United States had prepared contingency plans for stepping up diplomatic and military pressure on Nicaragua, Shultz said, "I do not believe that The New York Times fabricates stories. On the other hand, I know of no such plan."

Defense Secretary Caspar W. Weinberger, appearing on "Meet the Press (NBC-WRC), voiced concern about an arms buildup in Nicaragua and said the administration had "contingency plans," which he declined to outline. He cited the Monroe Doctrine, which in 1821 sought to bar European involvement in the Western Hemisphere, as the historic precedent for administration concern about the arms buildup by Managua.

Seeking to shift emphasis away from MiG warplanes that earlier in the week were reported as possibly being aboard a Soviet freighter in Nicaragua, Weinberger said, "There's never been any confirmation" that the warplanes were aboard the cargo ship. He said the "critical fact" is that "the Soviets are supplying a great deal of heavy offensive arms to Nicaragua, we think in an attempt to intimidate the Nicaraguan neighbors, who are the ones most obviously concerned about this.

"The United States is prepared for a number of contingencies that may have to be taken," he added, "and we're getting more prepared all the time."

Although the OAS is expected to debate the problem of security in Central America, officials here expect no major initiative on the issue during the six-day assembly. Nicaragua is represented here by Vice Foreign Minister Nora Astorga, who told reporters today that she intended to discuss the confrontation with the United States only on a private basis with other ministers here.

The discussion on economic issues followed a luncheon meeting including officials of the 11 Latin nations belonging to the Cartagena group, which formed earlier this year in the Colombian city of that name to consider joint action on the problems of their foreign loans.

The group agreed to press Shultz on its call for a special conference between debtor countries and western industrialized nations to discuss reforms of the international financial system. Officials said the Cartagena ministers were not satisfied with the Reagan administration's position that such talks can be carried out through existing forums such as the International Monetary Fund.

The General Assembly is the highest body of the OAS, a grouping of 32 nations of the Western Hemisphere that serves as a forum for discussion of regional issues and offers peace-keeping services in the event of conflict. The assembly is expected to last through Saturday.