More visibly this past week than before, President Ronald Reagan is being pushed, persuaded, and maneuvered by events back into the mainstream of American foreign policy as worked out by his three predecessors, Richard Nixon, Gerald Ford, and Jimmy Carter.
It is most obvious in respect to China. This was the week when Mr. Reagan signed a joint agreement with mainland China under which Washington agrees to reduce gradually its sale of weapons to Taiwan. In return China agreed that it will seek reunification of Taiwan with the mainland only ''peacefully.'' This was essentially the agreement worked out originally by Richard Nixon with China in 1972.
The same week witnessed an end to the bloodshed in west Beirut following the firm insistence by President Reagan that the Israeli offensive be stopped. Mr. Reagan's three predecessors had all found it necessary to put restraining pressure on Israel in order to keep open the possibility of an eventual peace between the Arabs and Israel.
It was appropriate and logical that the same week that saw these two developments also saw the publication of the first of two articles in the New York Times by Richard Nixon arguing that ''detente'' has been an abused and maligned word and that US foreign policy should head back down the road of what he calls ''hard-headed detente.''
Mr. Nixon specifically recommended the scheduling of annual ''summit'' conferences between the US and the USSR, a return to ''significant economic relations'' between the two countries, and a renewed search for limitations on nuclear weapons.
The Nixon advice included an end to the policy of trying to put economic pressure on the Soviets by such devices as the attempted blocking of the Siberian gas pipeline.
Mainstream US foreign policy of today dates largely from the Nixon-Kissinger era. It included a continuing diplomatic dialogue with the Soviet Union along with increasing trade. It achieved SALT I in nuclear weapons control and aimed at SALT II. It reopened US relations with mainland China and gave China priority consideration over Taiwan. It sought progress toward peace in the Middle East and used pressure on Israel toward that end.
Mr. Reagan campaigned for the presidency in 1980 on a foreign policy platform that repudiated every major feature of Nixon-Kissinger foreign policy. It promised to turn back to Taiwan from China, scrap SALT II, apply economic pressures on the Soviets, shun ''detente,'' and allow Israel to proceed with the annexation of the occupied territories.
The first 20 months of the Reagan administration have seen an attempt to apply campaign rhetoric to operating policy in all these areas.
The most obvious failure was in respect to Israel. The invasion of Lebanon could have been prevented. It was sanctioned by silence. It happened, and it produced widespread protest. Public criticism of what American bombs in Israeli hands were doing to people in Beirut forced the President to abandon permissiveness toward Israel.
The pro-Taiwan policy was heading into serious trouble. China began putting distance between itself and Washington. It made tentative moves toward re-normalizing its relations with Moscow. There was a danger that the Taiwan policy would push China back toward Moscow.
The policy of putting economic pressure on the Soviets was also running into serious trouble. The West European allies refused to go along with it. The attempted embargo on equipment for the gas pipeline from Siberia to Western Europe was repudiated individually by Britain, France, and Italy. On Aug. 12 the European Community issued a formal and official statement from its headquarters in Brussels.
That statement called on the US to abandon the embargo on pipeline equipment on the grounds that ''the European Community considers the US measures contrary to international law, and apparently at variance with rules and principles laid down in US law.''
Neoconservatives who backed Mr. Reagan in 1980 believe passionately in the idea of using economic pressure on the Soviets. Mr. Nixon aimed his pro-detente arguments at them. He said that ''those who would have us scuttle detente and return to a narrow confrontation are urging a form of unilateral disarmament. They would deprive us of our most effective diplomatic weapons.''
Mr. Nixon also contended that economic pressure on the Soviets would increase , not decrease, repression.
''An oppressive dictatorship is strengthened not weakened by external confrontation,'' Mr. Nixon contended. History tends to confirm him. Iran is a recent case in point. The Khomeini regime became the champion of the nation. The people rallied to the regime. It is today seated firmly in power.
The question is whether the hard-line, right-wing backers of Mr. Reagan in 1980 will be able to hold him to any part of their foreign policy program. They have lost on Taiwan and Israel. They may be losing on economic sanctions against the Soviets.
President Reagan is still marking time on summitry and on nuclear weapons. In theory, he is back in negotiations on nuclear weapons. In practice experts who watch these matters assume that the White House is not yet ready to make the concessions that would permit a new agreement. But events continue to work against Reagan campaign policy and to push Mr. Reagan back into the mainstream of pre-Reagan policy.
It is noteworthy in this respect that the new secretary of state, George Shultz, has been listening to veterans of mainstream policy, including Mr. Kissinger and Zbigniew Brzezinski from the Carter era.
The four-year term for American presidents can lead to confusion in foreign policy. The tendency, particularly when a change of party occurs, is for the newcomers to assume that their predecessors were wrong or foolish. It has taken Mr. Reagan nearly 20 months to learn that there were practical reasons for the policies he inherited.
Now he and his advisers are beginning to understand those policies, and even to listen to some of those who framed them.