The Organization of American States wound up this year's General Assembly session here yesterday following votes laying down guidelines for multinational companies operating in member nations and expressing "serious concern" over trends toward greater trade protectionism in developed countries.

Both resolutions were directed by implication toward the United States, by far the largest and wealthiest member of the 25-nation group, and the dominant force in Western Hemisphere commerce.

Along with a separate vote urging the United States to eliminate "prejudicial" duties on sugar imports, the resolutions were approved by all members of the assembly's economic commission, with the exception of the United States. They were expected to pass overwhelmingly in the final assembly vote scheduled for last night.

Economic issues vied with human rights for the focus of attention during this year's 10-day session, which OAS Secretary General Alejandro Orfila characterized yesterday as "less tense" than those of the recent past.

While the lengthy and often acrmonious debates between alleged human rights violators, including the governments of Uruguay, Paraguay, Nicaragua and Chile, and the more outspoken human rights advocates, such as Venezuela and the United States, continued, both sides this year seemed more to be going through a well-rehearsed and expected exercise than looking for confrontation.

In a similar spirit, the organization this year approved an antiterrorism resolution, proposed by a number of Latin military governments who have repeatedly justified their authoritarian regimes as necessities against out-side terrorists Similar resolutions were roundly defeated in last year's general assembly.

A proposed amendment, offered by Jamaica, which would have excluded southern African black nationalists from the terrorist condemnation, was defeated by the group.

While some private human rights activists critized the military governments for merely cloaking their continued rights abuses with more clever diplomacy. OAS spokesmen described this year's more subdued rights discussion as a step forward in "dialogue" between the group's human rights commission and the accused governments.

Almost since its inception in 1948, the OAS has been accused, by both its members and outsiders, as being an organization with no clear purpose and with a tendency to substitute long-winded speeches and reports for concrete action.

This year, however, many members said they felt encouraged over a new channeling of OAS energy into substantive economic areas.

The multinational guidelines approved by the essembly call on foreign companies operating in member states to abstain from all interference in the internal affairs of those states. The guidelines also maintain that the courts of those states have exclusive jurisdiction over their activities there.

The guidelines, whose very vagueness theoretically gives the member nations wide leverage in their treatment of the multinationals, ostensibly with OAS backing, were first suggested in 1974, and have been consistently opposed on several points by the United States.

In a position paper written in 1975, and attached to this year's OAS resolution, the U.S. delegation said it "could not support language" that gives the courts of other nations exclusive jurisdiction over the multinationals and excludes international law and the courts in the home country of the companies in question.

The resolution on trade protectionism reflects a growing fear throughout the developing nation of Latin America that increasing U.S. umemployments and a negative balace of payments will cause a tightening of U.S. markets for Latin exports.

The Latins, said one U.S. official, "want a sort of regional most-favored-nation bloc" in the Western Hemisphere, while the United States prefers to look at its trade relations in a "global" perspective.