PRESIDENT Reagan should feel rather good about his trip to China. He returned with his broad objectives - securing economic links for an expanding US-Pacific trade and huffing at the Soviet military threat from a Peking somewhat friendlier to Washington - comfortably in his pocket.
The President and Mrs. Reagan obviously enjoyed themselves. If ''goodwill'' still has meaning, the person-to-person side of the trip - from the gaggles of beautiful children and long phalanxes of officials to the private chats - had to be good for both the visiting Americans and their hosts.
Ignorance of adversaries breeds suspicion. It chills relations. Perhaps this is why Americans, in addition to the vicarious pleasure of seeing the American flag carried abroad, seem to want their leaders to travel. They are aware that this President on taking office had had rather less direct contact with foreign leaders and peoples than had other recent presidents.
Politically, Mr. Reagan can anticipate at least a momentary updraft in his popularity at home. Presidents customarily average a 6- to 8-point gain in public approval after such forays. In 1972, President Nixon's popularity rose 7 points after his China trip and 8 more for his Soviet trip - followed by a startling 17-point surge at the end of the year for the Vietnam settlement.
The Nixon precedent is instructive. By contrast, Mr. Reagan has no additional immediate Soviet card to play. Indeed, the President used his China outing to beat his administration's constant Soviet-threat drum in every major speech. In so doing, he ironically underscored that he was meeting with a secondary American adversary in Peking, and that relations with the No. 1 adversary, Moscow, remain deeply troubled.
Nixon in 1972, an election year, was preparing for detente with the Soviet Union. Further, there is no analogue today for the Vietnam war. At most, the Lebanon adventure, the Grenada landing, raised Vietnam echoes; the buildup of United States naval and land force in the Caribbean so far raises only intimations of direct armed conflict for Americans.
By such measures, the Nixon foreign policy initiatives a dozen years ago were bolder in diplomatic design, the American consciousness of foreign involvements far more deeply troubled.
The fact is, both the Soviet and American leaders are for the moment concentrating on their domestic agendas. The May Day parade in Moscow was devoted more to enshrining Mr. Chernenko as the new national leader than to criticizing the Americans. Mr. Reagan's repeated warnings in China of Soviet aggression - carefully censored from China's translated telecasts or carried full in inscrutable English - were partly intended for those in the President's audience back home who might worry that he had gone soft on communism.
Back in the United States, the Democrats were certainly cooperating with GOP ambitions. Gary Hart, his own candidacy slipping toward apparent defeat, reminded voters of the long, dispiriting Iranian hostage ordeal of four years ago, under the ''Carter-Mondale'' ticket. Some counterpoint to Mr. Reagan's chipper sojourn in China!
Serious security, economic, and political tensions remain in the Pacific. Some of the tensions are modern, some ancient. The Philippines is restive. Peking warns again of encroachment by Hanoi. The mismatch between Japan's economic and military might continues to build. US links with Thailand, Indonesia, need attention.
It would be foolish to suggest that in one six-day swing a US president, through a few cultural, tax, and nuclear facility agreements with Peking, and a visit to the Great Wall of China and an emperor's tomb, has reordered the course of relations among the multitudes loosely categorized as ''the Pacific Basin'' peoples.
But the White House still has many good reasons to be pleased - not the least a demonstrated willingness to attempt direct diplomacy as an alternative to impersonal projections of force abroad.