Chairman Hua Kuo-feng, making a symbolic break with China's centuries-old tradition of isolation, arrived here yesterday on a visit that underscored Peking's new and active involvement in world affairs.

In the first state visit made by a Chinese ruler west of the Soviet Union, Hua chose the Kremlin's Eastern European backyard to demonstrate support for President Nicolae Ceausescu and his maverick policy of independence from the Soviet Union.

Looking trim and vigorous, the 58-year-old Chinese leader received a tumultuous welcome that started with an exchange of kisses with Ceausescu and ended in a triumphant motor-cade through Bucharest.

Hundreds of thousands of Romanians lined the streets of the city, which reverberated with ceaseless cheers of "Hua, Hua" for nearly an hour.

At the entrance to the city, the open Mercedes limousine carrying the two leaders stopped for a brief ceremony during which Hua was presented the key to the city. The two men also left their car at Victory Square, in the heart of Bucharest, to join hundreds of Romanians dressed in colorful national costumes. Hua, his hands interlocked with those of young Romanian dancers, briefly joined in the "hora," raising his arms in the traditional gesture of friendship.

The carefully orchestrated reception seemed to fit the symbolism of the occasion.

The Chinese, who asserted that their goal is the establishment of a "united front against hegemonism" or Soviet domination, have chosen Eastern Europe for Hua's visit apparently to demostrate limits of Soviet power even in this region vital to Moscow's interests.

Diplomatic sources here said that even the timing of the trip was decided upon by Peking. Hua is to end his visit here and begin a seven-day call on President Tito of Yugoslavia Aug. 21, the date in 1968 when Warsaw Pact forces invaded Czechoslovakia to depose the liberal communist government of Alexander Dubel.

Although a member of the Warsaw Pact, Romania refused to take part in the Soviet-inspired action. Yugoslavia, which is nonaligned but ruled by a Communist government, was one of the severest critics of the invasion.

Beyond the ideological challenge, the development of close links with Romania and Yugoslavia fits Peking's policy of establishing ties with countries on the Kremlin's flanks. The Chinese are courting Western Europe and they have just concluded a "peace and friendship" treaty with Japan.

The Romanians have taken all possible precautions against giving the Soviets any tangible reason to take offense. An editorial on the front page of Scinteia, the party newspaper, yesterday said that China plays an important role in the struggle "against imperialism, colonialism, neocolonialism and any kind of domination and oppression."

By assertint that the Sino-Romanian links are based on "solidarity against foreign subordination and domination," the editorial came as close as Romania could afford to the Chinese concept of "anti-hegemony," or opposition to Soviet domination.

For the Romanians, Hua's visit is a demonstration of solidarity accompanied by implied pledges of assistance. While the Romanians are aware of risks involved, they have decided to press the limits of Soviet tolerance in the belief that the aging Kremlin leadership is currently preoccupied with Peking's global challenge as well as by deteriorating Soviet-American relations.

Despite outward signs of confidence, Romanian officials are going to great lengths to place Hua's visit here in a bilateral context. Hua and Ceausescu had conferred only three months ago during the Romanian's visit to China. Two high-level Chinese military delegations have since visited Romania. But all this is explained here as a normal dialogue between two socialist countries.

The reception accorded Hua yesterday was spectacular. The Chinese leader, accompanied by Vice Premier and Politburo member Chi Teng-kuei, Foreign Minister Huang Hua and 16 other officials, arrived at Otopeni airport at 10 a.m. The airport has been a virtual armed camp for several days with soldiers manning antiaircraft guns and access to the terminal controlled by the military.

Wearing a gray tunic, Hua, who is also China's premier, emerged from the Soviet-made IL62 jetliner. To avoid Soviet air space, the craft flew here via Iran, where Hua and his party stayed overnight. They are to make an official visit to Iran after Yugoslavia.

The airport was packed with party activists and Young Pioneers carrying flags and balloons. They were encouraged to cheer by the authorities as well as by the prospect of having a day off.

Hua and Ceausescu reviewed the honor guard and made no speeches at the airport. The entire ceremony was carried live on radio and television . A radio announcer described the meeting as one of "warm frienship."

Once the official motorcade reached the city limits, the streets were jammed with people waving Chinese or Romanian flags and bouquets of flowers. The government here organizes such outpourings of enthusiasm by taking people away from their jobs and assigning them to specific sections of the motorcade route.

On some avenues, youths in yellow gym suits performed various exercises as the motorcade passed. Elsewhere there were folk dancers and even a large group of Romanian girls doing Chinese dances with white scarves. The motorcade also passed in front of the Soviet Embassy here.

At Victoria square, in the shadow of the monument to Soviet soldiers who fell in World War II, large numbers of folk dance groups were gathered to entertain the visitor. Such officially organized welcoming activities and the size and enthusiasm of the crowds are carefully gauged for various occasions.

Official estimates of the size of the crowd yesterday was not available, but the number was certainly in the several hundredsof thousands.

Ceausescu later was host at a private lunch for Hua and the two men opened formal talks later at the former royal palace here.

Diplomatic sources here said that trade accords were expected to be announced during Hua's visit. The agreements will reportedly call for a double of the value of bilateral trade to $1 billion by 1980.

It is also reported that the two countries have discussed opening consulates in Shanghai and Constant. Yet, the opening of a Chinese consulate at Constanta, which is on the Black Sea and near major Soviet naval installations, would evitably be opposed by Moscow.

On the eve of Hua's visit, the Soviet Union voiced the belief that "the peoples of the Balkan countries will not permit this important region to be turned into an object of intrigues and threats of force which are dangerous for detente and the cause of peace." It also asserted that China's foreign policy is "deeply hostile to the interests of peace and socialism."

The statement was a part of the official communique on discussions between Soviet President Leonid Brezhnev and Bulgarian leader Todor Zhivkov.

Authoritative Soviet publications have criticized China's Balken policy by using a recent Albanian letter issued after China suddenly severed its ties with its former sole European client state.

The Soviets are quoting parts of the letter in which Albanians claim that the Chinese in 1968 and again in 1975 had urged Albania to set up a military alliance with Romania and Yugoslavia "because as a small country they could not defend themselves" against American imperialists and Soviet "hegemonists."