Belgrade — When Mika Spiljak arrives in Washington today to meet with President Reagan, many Americans will not know who he is. In fact, most Yugoslavs, when asked about their current leader, have to pause for a moment to come up with an opinion.
Mr. Spiljak has been fairly visible because of his role as president of the state presidency, a position that rotates every year. But even so, he is affected by the syndrome of anonymity that many Yugoslavs perceive in the system of collective leadership.
''They're all so faceless,'' a Yugoslav said. ''I think he's good. He's a family man who started out making shoes.''
Mr. Spiljak started his career as a shoemaker but quickly moved into trade-union work. He has held nearly every high Communist Party and government post, including prime minister.
The current Yugoslav leader's background is much like that of the late Josip Tito. Both came from Croatia, were workers who rose to power as self-made men, and fought with the partisans to liberate their country during World War II. But any similarities end there.
Spiljak has none of Tito's charisma or power. No one has filled the vacuum left by Tito almost four years ago, and Spiljak makes no pretense of doing so. He is the latest to serve as president in the collective system Tito left behind.
But a diplomat at the United States Embassy in Belgrade says Spiljak represents an important fact: ''The leadership system is running remarkably smoothly. Everyone knows who comes up next. The leadership may be undynamic, uncharis-matic, and uninspirational, but it is not unstable.''
The Reagan administration, like the Carter administration before it, considers Yugoslavia ''the linchpin in East-West relations,'' the diplomat said.
Because of its strategic location at the east end of the Mediterranean and its importance in the East-West balance in the area, the US wants Yugoslavia's stability to continue - especially now, during increased tension with the Soviet Union.
Both the US and Yugoslavia are touting Spiljak's visit as a ''continuation'' of their longstanding good relations. President Reagan accepted credentials from Yugoslavia's new US ambassador, Mico Rakic, last month and said he hoped for ''further expansion and improvement in our bilateral relations.''
The Spiljak visit also reaffirms US support during Yugoslavia's economic crisis. Yugoslavia owes Western creditors more than $19 billion and only escaped rescheduling last year because of a $4.5 billion, US-initiated Western bailout.
This year, Yugoslav officials are asking for another $3 billion to $3.5 billion.
Yugoslavia's 22 million people have seen their real incomes plummet 30 percent over the last three years. Exports to hard-currency countries increased some 27 percent last year, but overall production stagnated.
Even high party officials warn the party must not ignore worker dissatisfaction that could turn into political problems. So far such problems have been limited to nationalistic outbursts among a few of Yugoslavia's many ethnic groups.
The country launched a long-term economic reform plan last summer to try to unify the Yugoslav market. The economy is splintered among the republics and provinces, which have become largely autonomous under the devolution of power in the 1974 Constitution.
The party backed the plan, which allows for more ''macro decisionmaking'' in economics - most important, in the borrowing power of individual banks. The republics opposed the plan.
Despite the difficult times in Yugoslavia, Spiljak is generally liked. He has a reputation for speaking plainly and honestly and has not been identified with any faction. Because of his long years in the national leadership in Belgrade, he is perceived as being a ''federal man'' rather than representing any one republic.
Military balance in the Balkans is likely to be a topic for discussion while Spiljak is in Washington. Yugoslavia is not pleased with the NATO missile deployment in Europe, but the Yugoslav response has been very moderate.
For its part, ''the Reagan administration has actively responded to Yugoslav issues and concerns,'' the US diplomat said. ''Our relations are closer now than even under President Carter.''