For the world accustomed to the photographs of an ailing Mao Tse-tung receiving visitors inside Peking's Forbidden City, the sight of his hale and hearty successor globe-trotting in Eastern Europe is fresh and startling.

One senior diplomat, commenting on the unprecedented journey by Hua Kuo-feng to two European states, suggested that "by coming out of itself, China is going to turn global politics into a new ball game."

The Chinese have been a player in world politics, particularly since the onset of their bitter dispute with the Soviets. But under Mao, China was essentially an ideological power providing counterweight to those resisting Soviet influence.

Mao's imperial aloofness and cautious style in searching for allies and friends reflected China's continued isolationism.

But his successors in a relatively short period have injected dynamic elements into Mao's old policies marked by fear and hostility toward the Soviet Union. In doing so, they are searching for friends and allies against Moscow and doing it on a global scale.

The scope of this challenge, of Peking's goal to create a broad "united front" against Moscow, is underscored by the recent pronouncement of Chinese Defense Minister Hsu Hsiang-chien who asserted that "wherever the Soviet Union stirs up trouble, we shall support the people there to wage resolute struggle against it and destroy its tentacles."

The Chinese have used similar rhetoric in the past. But while these were mostly editorial attacks on the Soviets and pronouncements of a general nature, the new Chinese policy evolving this year is one of active involvement in world affairs.

Hua's visits symbolize this new trend. But his personal involvement was preceded by the following developments:

After six fruitless years of talks, China this month quickly completed a friendship and cooperation treaty with Japan. It includes a clause committing the two countries to oppose "hegemonism," the codeword for Soviet influence, in Asia.

Peking has stabilized its relations with the United States and improved ties with West European countries, urging them to strengthen NATO.

The Chinese have become more involved in African affairs. They have also extended diplomatic recognition to Oman, a Persian Gulf state they had previously condemned as reactionary, and to Libya, a Soviet ally.

Peking also established close relations with Yugoslavia, a nonaligned country whose brand of communism was once described by the Chinese as "dangerous revisionism." Since last September, more than 40 Chinese delegations have visited Yugoslavia to study its brand of "market socialism."

Before going to Moscow's East European backyard, Hua had visited North Korea to improve ties with that country.

All these steps indicate that Hua and his colleagues may be far less rigid than their predecessors and that they feel confident in pursuing an increasingly active role in gathering support for an anti-Kremlin alliance. The fact that Hua is to call on the shah of Iran on his way back to Peking suggests that the new Chinese leadership has no qualms about establishing ties with the man whom they had viewed as the epitome of reactionary forces.

Yet Hua's visit to Eastern Europe, and especially to Romania - a member of the Warsaw Pact - appears to be the most direct challenge to Moscow, which considers the region within its sphere of influence.

The challenge is apparently designed to test the limits of Soviet tolerance as well as to show the limits of Soviet power even in Eastern Europe.

Perhaps even more interesting is Romania's readiness to go along with the Chinese. The Romanians, who are known for their skillful diplomacy, are said to have sought to extend the limits of their independence because they view Moscow at this time as weak and preoccupied with the Chinese challenge as well as tensions in Soviet-American relations.

There is little the Soviets can do about Romania's actions, according to Western and Romanian observers here. The Kremlin, in this view, is preoccupied with the problem of succession to the aging leadership and the Soviets are believed to be in no mood to stage another Czechoslovak lesson.

Hence the Chinese may succeed in building up relations with the two Communist states in the Balkans and bring about a polarization among the ruling Communist parties while simulaneously building ties with non-Communist countries on the Kremlins's Flanks.

Moscow's anger has been obvious for some time. So far, however, the Soviets have only issued oblique warnings to Romania while attacking the Chinese pronouncements in general terms.