Washington — President Reagan's journey to the People's Republic of China had a predominantly diplomatic purpose. But there is little doubt the President will seek to reap political benefits from it during his reelection campaign.
''The trip was a genuine diplomatic initiative,'' a Reagan campaign official says. ''It was a complete success in terms of what the President set out to achieve - which was to start a personal dialogue with Chinese leaders and have an opportunity to talk about issues of world concern.''
''But it did fulfill a political purpose as well,'' the official says. ''It had a consistent message for constituencies at home - those who wanted an overture to China and those who wanted him to stand up for Taiwan. It's not a message we're displeased with.''
It is too early for polls to show how the American public reacted to the China trip. But Mr. Reagan's approval ratings continue to remain high, despite a number of domestic and foreign problems, including the unrelenting dilemma of Central America. Even many Democrats concede that the President is a formidable , perhaps unbeatable, candidate. According to a survey by the National Journal, a majority of Democratic state chairmen believe that Reagan has ''an excellent chance'' of defeating the Democratic nominee, whoever he turns out to be.
The China trip, in any case, is but one piece of a larger foreign policy canvas that the Reagan campaign will seek to exploit. A presidential trip next month to Ireland, to London for an economic summit, and to the beaches of Normandy for the D-Day anniversary will provide further opportunity to promote the President as a world statesman and leader. Not until after the European trip, however, will the President begin campaigning in earnest, campaign officials say.
When Reagan finally does go out on the hustings, his expedition to China will enable him to address two different domestic groups:
* To those conservatives who feared the President would abandon his strong support for Taiwan and opposed the PRC trip, Reagan can say that in China he stood up for American ideals - democracy, capitalism, religion - and did not give in to Chinese urgings for a speedier US reduction of arms sales to Taiwan. Even the Taiwanese government has reacted mildly to the results of the trip.
* To those Americans who have been concerned about the President's rigid anticommunism and the poor state of US relations with the Soviet Union, Reagan can point to the China trip as evidence of his diplomatic flexibility and ability to deal with communist nations on a pragmatic basis.
Some would add still another constituency gratified by the Reagan journey - Roman Catholics. En route home, in Fairbanks, Alaska, the President met with Pope John Paul II, who was himself en route to South Korea.Reagan has assiduously courted the Roman Catholic vote, recently establishing full US diplomatic relations with the Holy See.
From a few days before he went to the People's Republic, through the six days he spent there, Reagan dominated the news at home, nudging the Democratic race off the front pages. Nor has the public seen and heard the last of the China visit. The Republican National Committee had a film crew along on the trip, and reams of film are being processed.
No decision has yet been made about how to use the footage, campaign officials say, but it will be reviewed by the so-called Tuesday Team, the independent New York corporation set up to produce all paid media for the Reagan campaign. Eventually the material is expected to be used in paid commercials and perhaps at the Republican convention in August.
In substantive terms, China experts in and outside the administration count the presidential visit a success. While there were no departures from the positions of either side on such issues as Taiwan and no diplomatic breakthroughs, the President and Chinese leaders established a personal dialogue , candidly aired their views on a broad range of bilateral and global issues, and put the Sino-American relationship on a stabler, more solid basis. The door is now open for closer economic cooperation and, from the US standpoint, the groundwork is laid for drawing China more closely into the Pacific community as a counterbalance to the expanding Soviet presence in the region.
Some China-watchers express dismay that the President chose the occasion to criticize the Soviet Union - criticisms which the Chinese carefully deleted from their own media coverage. ''You don't go into a country and attack the Russians ,'' says one specialist. ''That clearly was designed for home consumption.''
Reagan's determination to speak to the Chinese about the virtues of democracy and free enterprise also struck some observers as diplomatically inappropriate and politically motivated. ''The Chinese handled his lecturing in a low-key way , '' China scholar A. Doak Barnett says, ''but Reagan's speeches did not enhance his reputation as a great statesman in the Chinese view.''
But the President in China seemed to be making a pitch as much to his own convictions as to domestic constituents. Asked during the trip if the Chinese minded his ''preaching'' about American values, he responded:
''They never said any word about that and I never put it as preaching to them. . . . I felt that if we're to get along, they've got to understand us, and what we believe. That's why I did that.''
However diplomatically awkward some of the President's remarks, the Chinese leadership also counted the visit a success. Huge crowds turned out for Reagan in Shanghai, the last stop on his itinerary. ''Such large crowds are not coincidence, for the leadership is concerned with form and symbolism and it ensures whether there are crowds or not,'' China expert Winston Lord, president of the Council on Foreign Relations, says. ''So Reagan did not hurt the United States by his comments about capitalism.''