Despite President Reagan's past reservations about relations with China, he was all smiles Tuesday when Premier Zhao Ziyang came to the White House. The warm welcome the Chinese leader received from Mr. Reagan under a cold, gray Washington sky reflected the distance the United States and China have traveled since the tense early days of US-China relations under the Reagan administration.
As a presidential candidate in 1980, Ronald Reagan leaned toward a policy of recognizing two Chinas, one with its capital in Peking and the other in Taiwan. He talked about a need to reestablish ''official relations'' with Taiwan. But despite a number of zigs and zags in his public statements over the past three years, Reagan has come to endorse a China policy that would have been unthinkable for him before he took office.
In his welcoming statement at the White House on Tuesday, the President spoke of Premier Zhao as a ''friend,'' praised China's modernization programs, and pointed to the ''flourishing'' trade between the US and China. He said that the two nations ''share many concerns'' and have much to learn from each other. In an apparent reference to the Soviet Union, Reagan said that the US and China ''stand on common ground'' in opposing ''expansionism'' and interference in the internal affairs of other nations.
Mr. Zhao, who was given full military honors at the White House welcoming ceremony, spoke of the importance of US-Chinese relations to the maintenance of world peace. He said that if the two sides ''strictly abide'' by their joint communique of Aug. 17, 1982, ''it is possible for China-US relations to leave behind jolts and uncertainties and embark on a smooth path.'' Under the communique that Zhao spoke of, the Reagan administration agreed to ''reduce gradually'' its arms sales to Taiwan, leading over a period of time to a final resolution of the Taiwan issue.
Reagan had shocked the Chinese early last year when, in an interview with the magazine Human Events, he seemed to minimize the importance of that joint communique. Since that time, however, the Reagan administration has reaffirmed its support for an expansion of US-China relations. Most important, it has placed China in the category of a friendly, nonallied nation for the purpose of transferring more US high technology to that nation. The Chinese had previously been treated much as are members of the Warsaw Pact when it came to high-technology exports.
Another potential obstacle to the development of relations arose last year when the US Senate Foreign Relations Committee passed a resolution urging a settlement of the Taiwan issue in a manner ''acceptable to the people of Taiwan.'' Further worsening the atmosphere, conservative US congressmen managed to slip an amendment into an appropriations bill supporting Taiwan's full membership in the Asian Development Bank despite Peking's application to replace Taiwan in the bank. The two moves appeared to jeopardize the Zhao trip to Washington.
But a personal statement by President Reagan at the end of November seems to have defused the tension. Reagan repudiated the Foreign Relations Committee formulation on Taiwan self-determination and restated the ''position of four successive governments that the People's Republic of China is the sole legal government of China.''
While Reagan and Zhao stood together on the White House podium Tuesday, they could hear the shouts of demonstrators advocating self-determination and independence for Taiwan. The crowd of several hundred demonstrators stood outside the fence to the south of the White House. Neither Reagan nor Zhao showed any sign of being bothered by the shouts.
This is the first good look Washington has had at the relatively young new Chinese leaders whom this and succeeding US administrations will have to deal with in China. Zhao, aged 64, is described by one administration official as the youngest member of the important Standing Committee of the Chinese Politburo. According to this official, he represents innovation, technical expertise, and a ''can do'' attitude.
As President Reagan noted in his welcoming statement, Zhao has been an ''eloquent'' advocate of modernization and reforms. But there are, of course, other schools of thought in China. Hu Yaobang, the Communist Party secretary, is thought by some to be arguing in China's policymaking councils for a harder line toward the US and the West in general.
Zhao is known to have a spontaneous sense of humor and an ability to be engaging, both qualities that tend to have appeal for Americans.
As Prof. Kenneth Lieberthal at the University of Michigan notes, Zhao is the first member of the Standing Committee of the Politburo to wear a Western tie and jacket in public, instead of the standard gray Mao suit, since before China's Cultural Revolution. He wore a white shirt and blue tie to the White House meeting.
But the engaging manner sometimes yields to a tougher style. Chinese sources said that in his October 1981 meeting with President Reagan in Cancun, Zhao sternly lectured to Reagan over what the Chinese considered to be faults in the administration's attitude toward Taiwan and various third-world issues.