The last week of September brought us a qualified respite from world tensions. At time of writing, there was a pleasant relief from fighting in Lebanon. The cease-fire removed, at least for a while, the danger of a Soviet-US confrontation there.
President Reagan used his annual speech at the United Nations primarily as a vehicle for announcing a modest change toward flexibility in the United States position on nuclear weapons. He also got in a reference to the Soviet shooting down of the Korean airliner and a suspicion of Soviet violations of SALT II. But those were minor themes. His emphasis was on his professed desire for accommodation and peace.
The news broke, out of Peking, that Mr. Reagan will go to China for a visit in the spring, in April. China's prime minister will first come to Washington in January. It is to be remembered that when former President Richard Nixon reopened US relations with China in 1972, the sequel was an easing of relations with Moscow. The effect was to build a new element of stability into world patterns.
President Reagan committed himself publicly and vigorously to an increase in US funding for the International Monetary Fund. This, on top of the new flexibility on nuclear weapons, made Washington's friends and allies a little happier.
The change in nuclear arms position helped to undercut the ''peace movement'' in Europe. It reduces the prospective police problem, particularly for West Germany. Street demonstrations against NATO's new US nuclear weapons, due to start deployment in December, have already begun to gather steam.
That could be one reason, of course, why the Reagan speech drew such a stinging response from Yuri Andropov. The Soviet leader has been doing his best to encourage the peace movement in order to undermine the planned missile deployment. But the Kremlin's supposedly dovish feathers are looking a bit ruffled these days, not least after the demise of the Korean airliner.
While nothing can eliminate political maneuvering in Washington between Democrats and Republicans, still the degree of heat in the process was reduced by the cease-fire in Lebanon. For the moment the question of the War Powers Act became moot. So long as there is a cease-fire among Lebanese factions, the US Marines along the coast are not caught up in hostilities.
Congress has no serious objections to US Marines being in Lebanon as observers of a cease-fire. What worries Congress is the possibility of deeper involvement in fighting.
Matters in Lebanon had been getting dangerous during the preceding week. Syria was actively on the side of the Druze and Shiite factions battling the Lebanese Army. The marines were returning fire. They were taking an active role in fighting. They were shooting against a faction of Arabs that is backed by Syria, which in turn is backed by the Soviet Union. There are many Soviet troops in Syria.
The Middle East is an area where US and Soviet interests are directly in conflict. Both have what they consider vital interests in the region. The US backs Israel. The Soviets back the Arabs against Israel. Any fighting in the Middle East which includes US troops is likely to include Soviet troops as well, sooner or later.
During the 1973 war the Soviets prepared to send airborne troops to the aid of an Egyptian Army surrounded by the Israelis. US armed forces were put on a ''condition 3'' alert, worldwide. That sort of thing can happen again anytime there is trouble in the Middle East. Neither Washington nor Moscow would accept domination of the area by the other.
This past week found the Arabs able to reach agreement on a cease-fire in Lebanon. The possibility is opened up that the various warring Arab factions in Lebanon can work out a new arrangement among themselves and proceed toward setting up a new government. It will be very difficult. But with a cease-fire it could conceivably be done.
The most intriguing event of the week was the announcement that Mr. Reagan will go to China in the spring. It was preceded by US Secretary of Defense Caspar Weinberger telling the Chinese in Peking that they may now buy technology which they want to use in modernizing their industry. Some would also be useful in modernizing weapons for the armed forces.
The Chinese have resented the barriers which until now have denied them access to much modern US industrial technology. They also resent continued US support to Taiwan. Mr. Weinberger must have overcome at least some of that resentment for them to agree to let Mr. Reagan come to China.
It presumably also means that Mr. Reagan has reconciled himself to the idea of the US dealing with the Chinese government in Peking on a friendly and cooperative basis.
Mr. Reagan came to Washington preaching a revival of US relations with Taiwan. That would have meant reversing the attitude toward the two Chinas which Mr. Nixon originated and which his successors, Gerald Ford and Jimmy Carter, carried along.
The launching of that policy in 1972 had a galvanic affect on Moscow. When Mr. Nixon completed his dramatic visit to Peking, he went on to Moscow. Never was an American president welcomed so effusively - and never, before or since, have the Soviets been so eager to work out easier relations with the US.
Events since Mr. Nixon arrived in Peking justify a general rule about world affairs. The closer Washington and Peking, the more restrained and careful is Moscow. But when Washington and Peking are quarreling, Moscow feels freer to be bold and adventurous.
Will Mr. Reagan take a page from the story of Richard Nixon?
If he knows that story and if he recognizes that nothing worries the Soviets quite as much as closeness between Washington and Peking, well, he might want to go to Moscow - after Peking.
April may be an interesting month.