* Over the last four years Americans have become more confident about the state of US military security. They favor keeping defense spending at current levels rather than increasing it.
* While distrust of the Soviet Union remains strong, the US public and its leaders generally would like the two countries to reestablish cultural and economic ties (though limiting computer sales) and continue work toward an arms agreement. A strong majority would favor a freeze ''now,'' if the Soviet Union agreed.
* In rating world leaders, Pope John Paul II, British Prime Minister Margaret Thatcher, and Canadian Prime Minister Pierre Trudeau were in top place. Secretary of State George P. Shultz, in fourth place, ranks one notch higher than President Reagan. Among countries: Canada, Britain, France, and Mexico hold top warmth ratings. Though Cuba ranks near the bottom, there is substantial public support for renewing economic and diplomatic ties with that country.
These are among the key findings in a nationwide survey conducted by the Gallup Organization for the Chicago Council on Foreign Relations. The poll, touching base with 1,546 citizens and 341 leaders in government, academia, and private enterprise, is the third taken over the last eight years. It was released as the US foreign aid bill was pending in Congress.
One of the most ''astonishing'' conclusions, according to Chicago Council on Foreign Relations president John Rielly: Though the peaceful coming to power of a Communist government in such nations as Mexico and Saudi Arabia would be viewed as a ''great threat'' to US interests, a similar event in nearby El Salvador would be viewed as not much of a threat at all. Less than a majority of those interviewed would even favor sending military aid there.
''One would have thought there would be a much greater willingness to get involved,'' says Mr. Rielly. ''No doubt it does reflect the Vietnam experience.''
Yet he notes that the survey shows strong continuing support for NATO and a willingness among Americans to use troops in certain crisis situations, such as a Soviet invasion of Western Europe or of Japan.
Though the great majority said they thought the US has been a ''force for good'' in the world since World War II, a slim majority agree the national interest requires active participation in world affairs by the US. And more than one-third says it would be better if the US ''stayed out'' of world affairs.
Indeed, the public rating of US handling of most recent foreign-policy crises (Soviet invasion of Afghanistan, imposition of martial law in Poland, the situation in El Salvador, Israeli invasion of Lebanon, US hostage crisis in Iran) ranged from fair to poor. Only the Falklands crisis, in which the US played a minimal role, earned a positive rating.
The feeling that the US would fare better with less rather than more involvement also shows up strongly in limited support for foreign aid. Despite Secretary of State Shultz's recent efforts to play down economic aid costs, barely half of the public favors giving any economic aid at all and more than half oppose the giving of military aid or selling military equipment. The survey shows a much higher percentage is interested in protecting jobs at home.
The Middle East, as in past surveys, remains the major foreign-policy problem , in the view of most Americans. The majority disapprove of Israel's recent actions in Lebanon, favor the President's Mideast peace plan by a strong margin, and support formation of an independent, separate Palestinian state.