Few qualities are as highly prized in Balkan politics as the ability to stay on near the summit of power for a long period. Yugoslavia's No. 2 man, Edward Kardelj, has been a master practitioner of the art.

Kardelj, who arrives in Washington on Wednesday on his first official visit to the United States, has lived in President Tito's shadow for more than 40 years as a faithful lieutenant and councellor. Now, as the Yugoslavs prepare for a change of guard after Tito, who is 85, Kardelj is generally considered to be his most likely successor.

A former schoolteacher from the northwestern republic of Slovenia, Kardelj, 67, is the most influential survivor from the inner circle of Communist partisans who fought with Tito during World War II. Most other members of this small, tightly-knit group are either dead, in semi-retirement, or like the writer Milovan Djilas and the former secret police chief Alexander Rankovic, disgraced.

Although he suffers from bouts of ill-health and has largely withdrawn from the problems of day-to-day administration, there is no question that Kardelj is now the No. 2 man in Yugoslavia. He is a member of both the nine-man collective state presidency and the presidency of the Communist party. Other posts he has held during has long career include those of vice-president and foreign minister.

In the event of Tito's death, it is believed in Belgrade that Kardelj would rapidly become the dominating figure in the state presidency, while he fellow Slovene and former protege, Stane Dolanc, 51, would look after the party organization.

Kardelj is in the unique position of being acceptable to nearly all other Yugoslav national leaders, not just because he has been around for so long but also because of his reputation for settling disputes tactfully. He gives the impression, unusual for a politician, of being genuinely interested in the pursuit of power.

His would certainly be a very different style of leadership to the charisma and personality cult that surround Tito. In a rare interview before leaving for the United States, Kardelj revealed that he enjoys reflective pursuits like gathering mushrooms (of which hs is an acknowledged expert), fishing in mountain streams, and listening to his large collection of classical records. He also likes being with his three grandchildren.

By contrast, Tito spends much of his spare time hunting animals and looking after his magnificent wine cellar. The two men also differ in their style of oratory. While Tito is always earthy and to the point, Kardelj tends to wrap his thoughts in ideological abstractions.

Beneath Kardelj's mild manner and courteous appearance, however, there is clearly a man of enormous determination. One reason why Tito chose him as one of his closest collaborators during the 1930s was that he did not give information to the police while under arrest, despite being badly treated. He was also, along with Tito, one of the Yugoslav Communists who studied in Moscow and survived the Stalinist purges.

According to local gossip, there are few Yugoslav politicians more disliked by the Soviet leadership than Kardelj. This is because he was largely responsible for providing a coherent theoretical basis for Yugosalvia's defiance of Stalin in 1948. By dreaming up the idea of workers' self-management, Kardelj mapped out an alternative road to socialism that continues to be an inspiration to other Communist parties seeking greater independence from Moscow.

Perhaps understandably, therefore, Kardelj was reluctant to analyze Yugoslavia's present relations with the Soviet Union in detail.

During the interview, Kardelj revealed that an amnesty, probably including the release of some political prisoners will most likely take place on Nov. 29, the Yugoslav national day. Earlier this year, senior Communist officials spoke of a large-scale amnesty to concide with the May Day celebrations but it was postponed, apparently to avoid the impression that Yugoslavia was giving way to pressure over human rights from the west.

Asked about alleged human rights violations in Yugoslavia, including the refusal of a passport to Djilas and the imprisonment of the dissident writer Mihajlo Mihajlov, Kardelj replied that only "a relatively small number of people" are kept in prison for political reasons.

Kardelj said restrictions on the issuing of passports are minimal. "I must say that fewer people in Yugoslavia have difficulties in getting a passport than in the United States. In fact, Yugoslavia is one of the most open countries in the world," he said in his modest office in a government building in Belgrade.

In reply to a question about the broader aspects of President Carter's human-rights policy, Kradelj said that Yugoslavia did not object in principle to human rights being discussed since no country could claim to have a completely clear record. But he warned of possible dangers if the debate was turned into an instrument of foreign policy or ideological struggle between the two blocs.

Ideological problems have always been, and remain, Kardelj's chief interest. He was one of the pioneers of the theory of nonalignment, which was given practical shape at the first conference of nonaligned nations that met in Belgrade in 1961. It was a course that has won Yugoslavia valuable support from developing Asian and African countries.

Kardelj welcomed the interest shown by China in the nonaligned movement during Tito's recent visit to Peking, but was clearly alarmed by conflicts between individual nonaligned countries. He said such disputes, particularly in Africa, indicate a struggle for influence between the two blocks that makes solutions more difficult.

"However, I believe these are only temporary crises," he added.

During his week-long stay in the United States, Kardelj will be the guest of vice-president Mondale, who visited Belgrade in May. He is also scheduled to meet President Carter and congressional leaders.