Bolivians will go to the polls to vote for a president Sunday, but while it is certain there will be a change in government, there is no guarantee that the new regime will be headed by the candidate they elect.

In this sparsely settled country of five million, which by some counts has had 189 coups, attempted coups and changes of government since independence from Spain 154 years ago, voters seem to be talking less about who will win the presidential race than about when the next coup will come.

After originally vowing that they would not let elections take place at all, then asking for a one-year postponement "to reorganize" the country -- turned down by interim president Lydia Gueiler -- the Bolivian military has now indicated that it will wait and see who the winner is.

Possibily the worst outcome would be that none of the 13 presidential hopefuls would gain the necessary majority. In that case, the new Congress, which also will be elected Sunday, would have to choose a president when it convenes in August.

Although the capital has been almost unnaturally calm during this round of campaigns following the political upheavals of the past eight months, several campaign rallies were broken up by bombings, including one in which presidential candidate Hernan Siles Zuazo barely escaped with his life.

Another leading candidate Gen. Hugo Banzer, already has said that one of the country's "national institutions," presumably the military, will step in and take control if the right candidate does not win.

Both Siles and Banzer, as well as another leading candidate, Victor Paz Estenssloro, are former presidents. Nevertheless, there is a surprisingly wide, if somewhat confusing range of choices.

Another candidate is a full-blooded Ayamara Indian, whose colorful ear-flapping stocking cap and layers of wool sweaters that protect against the mountain cold show his connection with Bolivia's peasants, the highland people who make up almost two-thirds of the population. His platform calls for changing the name of the country to Kollasuya, the ancient Inca name for the region, and making Aymara the official language.

On the far right, the candidate for the Socialist Falange Party of Bolivia was once an active member of the Communist Party.

Leftist voters here might find it particularly difficult to decide where to put their "X" on the rainbow ballot that has a different colored column for each party.The pro-Soviet wing of the Communist Party is supporting leftist Siles, while the Chinese-oriented faction is backing the centrist candidacy of Pax Estenssoro. Meanwhile, the Socialist Party candidate is without any Communist Party patronage.

Elections were held under Banzer in 1978, but they were contaminated by such fraud that even the winner asked that they be annulled.

Two bloodless coups followed before election round number two in 1979. The winner was Siles, a leader of the 1952 revolution that resulted in universal suffrage, nationalization of most the country's natural resources and a breaking up of some of the largest estates. Only 1,512 votes back was Paz Estenssoro, a three-time president who was deposed by a military coup in 1964.

A distant third last year was Banzer, who was being investigated by the recently recessed Congress for a long list of alleged fiscal crimes and human right violations.

When no one received a majority of the popular vote, Congress, exercising its constitutional powers, elevated one of its own, Walter Guevara Arze, to the presidency. Guevara lasted just 10 weeks before being deposed by one of Bolivia's ambitious, conservative Army officers, Col. Alberto Natusch Busch.

After 16 violent days during which soldiers killed more than 200 unarmed civilians, Natusch was forced to flee and Congress put Gueiler in the palace. Gueiler is not a candidate this year.

In addition to the civilian aspirants, it is no secret that several colonels and generals think they should occupy the presidential chair.

It is now widely accepted that the United States played a significant role in preventing a coup in late May when Ambassador Marvin Weissman warned that the Americans would cut off all economic aid -- $200 million in 1980 -- to a military government.

Although publicly denying he was ever plotting a coup, the commander of the Army, Gen. Luis Garcia Meza, demanded that Weissman be expelled from the country for interfering in Bolivia's internal affairs.

The military's anti-American campaign has been supported, strangely enough, by the right.

Bolivian politicians and political observers generally believe that right-wing elements are using the Weissman incident and violence to create the civil disorder that would justify a military takeover.