All three candidates in Boliva's recent presidential election apparently received substantial sums of money from foreign sources, reflecting the growing international interest in the slow return to democracy in Latin America.

Despite the country's remote location and its considerable socail and economic problems, a number of nations, including the United States, the Soviet Union, China, Venezuela, Cuba and Argentina have taken more than a passing interest in Bolivia's political transformation, according to well-informed Bolivian and foreign analysts here.

In addition, political organizations with international interests are known or suspected by diplomats here to have contributed to one or another of the three coalitions that supported candidates in the July 1 election. They include the West German Social Democrats, the Venezuelan Social Christian COPEI party, and the Montoneros from Argentina.

For both the Carter administration and the Venezuelan government of Luis Herrera Campins, the political situation here is important because both countries are committed officially to encouraging democratic governments in Latin America.

On the other hand, neighboring, military governments worry that a new climate of political openness in Bolivia could affect their own countries, according to diplomatic observers.

For this reason, Bolivia's five more powerful neighbors -- Aregentina Brazil, Chile, Paraguay and Peru, all undrr military rule -- are known to be watching political developments here very carefully.

The best circumstantial evidence that foreign funds helped finance Bolivia's recent election, observers here say, is simple arithmetic.

None of the three major political groupings here -- the National Revolutionary Alliance of Victor Paz Estensoro, the Democratic Popular Union of Hernan Siles Zuazo and the National Democratic Alliance of Gen. Hugo Banzer Suarez -- thad the ability to raise substantial funds from their rank-and-file supporters in this poorest of all South American countries. et each party was able to spend upwards of $1 million and possibly, in the case of Siles' group, as much as $2.5 million, according to estimates made by politically active Volivians and confirmed by Western diplomats here.

It is known from well-informed Bolivian sources that the Christian Democratic Party here, which is part of the Paz coalition, received $240,000 from the COPEI party of Venezuelan President Herrera Campins. Paz may also have received some money, although probably not very much, from China, funneled through the Communist Marxist-Lennist Party, which was also part of the Paz coalition, according to diplomatic sources.

One of Paz's principal fund-raisers said that most of the $1.4 million sent by the centrist Revolutionary Alliance, however, came from private interests in Boliva, including a substantial contribution from one foreign firm that has a lucrative import monopoly here.

Speculation that the Paz coalition received money from the CIA was categorically dismissed by a well-informed diplomatic source.

Diplomatic observers believe that the Sile campaign spent between $1 million and $2.5 million, which it received from a variety of sources. Among the donors were some Bolivian businessmen who actually preferred Paz but hedged their bets by contributing to the leftist Siles, whose coalition led in unofficial final returns published last week. Paz Estenssoro, however, appears to held an edge in congressional seats, having gained a plurality in seven of nine provinces.

The newly elected Congress must meet Aug. 2 to choose a president among the three front-runners, since none of them won an absolute majority.

Siles' primary source of foreign funds was West Germany's Social Democratic Party, which channeled the money through the Portuguese Socialists of Mario Soares, according to both Bolivian and diplomatic sources.

These sources also believe the Bolivia's Revolutionary Left Movement which was part of the Siles coalition, received support from radical groups that may have included the Argentine Montoneros, based in Paris, the ERP, another Argentine guerrilla group, as well as the Cubans and Libyans.

One of the movement's top leaders, Antonio Aranibar, denied that "we received money from anyone" outside Bolivia, although he declined to answer when asked if the Siles coalition receive money from the West German Socialists.

The Siles coalition also included the Communist Party of Bolivia, which Western diplomats said probably received about twicce its $200,000 annual subsidy from the Soviet Union in order to compete effectively in the campaign. About 10 Communists were elected to Congress on the Siles ticket.

Banzer, Bolivia's rightist military leader from 1971 until he was over thrown last year, spent substantial sums of money which, it is generally agreed, came from his own pocket and those of other generals and businessmen who enriched themselves during his seven years as president.

Some diplomatic sources and political opponents of Banzer here believe that he also received money, directly or indirectly, from Argentina's military government because of its close ties with the strongly anticommunist Banzer.

One source with close contacts in the Argentine military said the currnet ruling junta in that country is convinced that there are ties between Bolivia's Revolutionary Left Movement and Argentine guerilla groups. Diplomatic observers said it was likely that the Argentines would have helped Banzer, hoping that he would gain enough strength within the new democratically elected Congress to forestall any effort to allow Argentine guerrillas to use Bolivia as a base of operations against neighboring Argentina.