October 19, 1981

Greece's Socialist opposition won a major victory in parliamentary elections today, bringing an end to 35 years of pro-Western conservative rule. Prime Minister George Rallis conceded defeat after early returns showed that the Panhellenic Socialist Movement of Andreas Papandreou had taken a commanding lead in most parts of the country. ''We will not lead the country into any adventure,'' Mr. Papandreou, the son of George Papandreou, a former Prime Minister of Greece, said in a victory speech. The Socialist victory, achieved with strong backing in the countryside, could mean radical change in this country's foreign policy since the party's program expresses opposition to Greece's membership in the North Atlantic Treaty Organization and the European Economic Community and to the presence of American bases here.

The Jets achieved one of the startling upsets of the season yesterday by trouncing the Buffalo Bills, 33-14, at Shea Stadium. ''There was a Remember Pearl Harbor syndrome around here,'' said Marvin Powell, the right tackle, alluding to the opening game of the season, when Buffalo embarrassed the Jets, 31-0. Yesterday, the Jets relied on opportunism, quarterback pressure, bizarre plays - things that opposing teams used in victories over them. And even though Bruce Harper did not prove he could count backward, he still played a key role in the game - a game that ended with Mark Gastineau, the defensive end, refusing to leave the field, waving to the crowd, demanding to hear their applause.

Bowing to Congressional opposition, White House officials agreed today to trim by more than half the $13 billion package of new budget cuts proposed for the 1982 fiscal year, which began Oct. 1. At the same time President Reagan said the nation's economy was in a ''slight'' recession. At a White House meeting, key Reagan Administration officials and Howard H. Baker Jr., the Senate majority leader, also agreed to a measure that would produce more than double the amount of new revenue that the President had proposed, according to Congressional and Administration sources. The White House officials agreed to seek $5 billion to $6 billion in new budget cuts, according to an aide to the Senate Republican leader and a spokesman for the Office of Management and Budget. These would take the form of reductions in discretionary appropriations, these sources indicated.

Nine months ago President Reagan pledged to end the recent pattern of Administrations speaking with conflicting voices on foreign and military policy. But there are still mixed signals and there is still no disciplined system for making decisions in these areas, according to Administration officials, legislators and foreign diplomats interviewed over the last month. Mr. Reagan said that he intended to solve the problem by downgrading the role of the national security adviser, upgrading that of the Secretary of State and re-establishing an orderly decisionmaking system. But dozens of officials who were interviewed said his efforts had not yet succeeded. ''You can see my frustration,'' said a senior Administration official. ''Cabinet government works on the domestic side, but there is nothing comparable on the national security side.''

What is expected to be the largest and most complex arbitration process ever conducted gets under way this week as an international tribunal convenes to accept the claims of American corporations that did business with Iran before the fall of the Shah. Carpenters have been hastily working to complete shelving here in the Peace Palace's Court of Arbitration, where as many as 2,500 claimants are expected to file depositions seeking more than $1 billion in compensation for expropriation of assets, breach of contract or unpaid debts. ''There have been claims tribunals after wars, in Coblenz between Germany and the Allies after the World War, and between Mexico and the United States many years ago,'' said Gunnar Lagergren, the 69-year-old Swedish jurist and expert on international arbitration who will lead the tribunal. ''But the size of this and its complexity makes it rather extraordinary.''