Prospects for change at the top fascinate Asia-watchers

''Who will rule next?'' The question of succession has become an ever-present concern of diplomats, journalists, businessmen, the military, and intelligence officers involved with Asia.

Behind it is the widespread but sometimes unwarranted assumption that change at the top may heavily influence an Asian country's economic and political relations with outside governments and corporations.

This is a common problem for the foreign business and diplomatic community in almost any country. But it's worse in Asia, because the region's political and cultural traditions are so unfamiliar to the West.

Political maneuverings in Asia, which lacks the West's democratic tradition, sometimes strike outsiders as ''unpredictable or ''inscrutable.'' In China, Vietnam, the two Koreas, Taiwan, and Singapore, personality cults have elevated leaders into nearly indispensable father figures. This raises concern that no successor could fill their shoes without instability or major economic and foreign policy changes.

Some Asians themselves are perplexed by the succession question. Still, they can be amused by the great emphasis placed on the issue by foreign observers. Asians sometimes point out that their countries are no more unpredictable than other nations. They point out that many Asian leaders stay in power far longer than their Western counterparts.

Asia's ''West-watchers'' are sometimes puzzled at what they see as erratic, unpredictalbe, extreme swings in Western policies that sometimes result when an election or parliamentary maneuvering ousts an incumbent. In Asia, where security and economic vitality may be heavily influenced by just who wields power in Washington, the United States succession question may seem just as important as any issue in Asia itself.

US corporations pay as much as $2,500 a year for ''political risk'' reports from consultants who combine scholarly social science diagrams and research with journalistic brevity. Governments such as that of the US want to know just how likely it is that the weapons assistance and other aid granted will fall into the hands of a government that later turns hostile. The US, for example, wants to know just how secure its base facilities, such as the Subic Bay Naval Base and Clark Air Force Base in the Philippines, are.

In the wake of communist victories in China and Indochina there has also been a concern over any possibility that other countries would adopt communist or socialist systems unresponsive to Western corporations. China's open-door policy of cooperation with foreign companies under Deng Xiaoping has raised the question of whether those doors are likely to remain open after Mr. Deng's passing.

Besides major nationalizations and foreign policy realignments, there are subtler issues, too. What guidelines will develop for dealing with foreigners, either under a strong new leader, or after a period of anarchic infighting? Will tax and price policies, for example, be changed to win popular political support for military or civilian figures contending for power? With a power struggle in progress, will higher- and lower-level officials be reluctant to risk retaliation by making decisions and negotiating with foreigners? Will a new military ruler try to rally nationalistic support by clamping down on foreign commercial activities? Or will a democratically elected government of civilians be so divided into factions and parties that its economic policies will change unpredictably?

Changing answers to these questions may influence foreign companies to concentrate on short-term, medium-term, or long-term investment. A foreign government concluding that a current leader is on the way out may want to put out feelers to a possible successor.

The succession question in part reflects the interaction of regional traditions with Western influence. Much of the region only recently emerged from the post-nationalistic struggle that threw off Western and Japanese rule.

In much of pre-colonial Asia, there was some idea that a ruler should serve, if not represent, the interests of his people. But leaders most often gained their power from family lines, conquests, or educational or economic position. In many countries ideas of benevolent paternalism supported authoriatarian tendencies both in family and government.

European colonialism governed most of East Asia, with the exception of Japan, Thailand, and, in name at least, China. Colonies frequently were not unified nations, but collections of different races, tribes, and religious groups that might have remained separate except for colonial rule.

This meant that a strong leader was sometimes needed to prevent inharmony, rebellion, or civil war after independence. ''Keeping the lid on'' with authoritarian rule could be justified as necessary to preserve peace and harmony - not simply to maintain the leader's personal power.

''He who rides the tiger dare not get off,'' is another variation on this theme. A ruler who was insufficiently vigilant against ruthless opponents could find himself deposed, and perhaps executed.

Nationalist movements that came to power after World War II were sometimes held together more by their opposition to colonialism than on what to do next. This bred military revolutionary strength and spirit, rather than administrative skill (China, Indonesia, and Vietnam). It emphasized military power and the cult of personality (under Sukarno in Indonesia, Mao Tse-tung in China, and Ho Chi Minh in Vietnam), rather than constitutional rule.

Concepts of constitutional rule did filter in, often from Koreans, Indians, Chinese, Japanese, and Filipinos who studied in the West or studied in foreign or missionary schools at home. But in many Asian countries these ideas are stil seen as ''foreign,'' inappropriate, or even subversive of order, harmony, and Asian ways.

Late 19th-century Japan imported limited German-style constitutionalism, and US-occupied Japan received an American-style constitution after postwar occupation. American colonialism left a US-style constitution in the Philippines which lasted until President Ferdinand E. Marcos declared martial law in 1971.

It is thus not surprising that in Asian countries from China to the Philippines there is often no clear constitutional path by which one leader replaces another. Often real power is transferred by behind-the-scenes maneuvering, army support, or even by coup d'etat, rather than by formally ordained and legally constituted means. Law is used to justify and effect power changes - rather than to govern the procedures by which power changes.

Where constitutionalism has survived, it has adapted to local ways. What political scientist Robert A. Scalapino once called Japan's ''one-and-one-half party system'' has long been dominated by the ruling Liberal Democratic Party. Different party factions contend for power by maneuvering to negotiate a consensus. British-influenced India also has a parliamentary system. But the ruling Congress Party is seen by some as largely held together by the personal political skill of Indira Gandhi. Much will depend on whether the Congress Party will remain united enough after Mrs. Gandhi to unify India. In Bangladesh and Pakistan, coup d'etat followed by army rule are recent methods of power transfer.

In some Asian countries, leaders have personally chosen successors in advance. In the early 1960s Mao Tse-tung chose Liu Shaoqi. By the late 1960s Liu had been replaced as successor by Lin Biao, who himself fell from favor and was reported killed in a 1971 airplane crash.

But Asian leaders are sometimes reluctant to delegate power in advance. Without such delegation, a successor may lack the clout and experience to consolidate power after a leader's passing.

One possibility is a new power struggle in which rivals of the leading contender temporarily unite to prevent him from establishing his power. In China after the passing of Mao, Hua Guofeng united with supporters of the previously purged Deng Xiaoping to depose Mao's widow, Jiang Qhing, and three other members of the ''gang of four.'' But later Hua was eased from power, after Deng had been promoted to China's most important leader.

Chairman Deng Xiaoping is now seen as grooming a younger generation of leaders headed by Communist Party Secretary General Hu Yaobang to take over eventually. But a question is whether this new group will be able to build its own power base soon enough to be fully in control after Deng departs the scene.

In Taiwan there is as yet no clear indication of who will replace President Chiang Ching-kuo. A ''cult of personality'' now identifies Taiwan's prosperity with the personal leadership of the President.

In authoritarian Singapore and communist North Korea, heirs apparent are declared from time to time. But the concentrated power of Lee Kuan Yew and Kim Il Sung makes it uncertain how well their chosen successors can ever fill their shoes.

In the Thai monarchy, civilian political parties vie for power with army commanders in a subtle process of bargaining that sometimes includes elections and coups. In Malaysia, parliamentary government is overshadowed by the strong security powers maintained to contain communal conflicts among Malays, Chinese, and Indians. In Laos, Kampuchea, and Vietnam, leaders emerge from communist parties, governments, and army.

In the Philippine, President Marcos's 1972 declaration of martial law largely eliminated the US-style constitutional framework left over from American colonialism. There is no established, tested procedure for determining what will happen after Mr. Marcos's passing. Speculation thus centers on the posibility that the military - or military-backed economic technocrats - may take over.