Former military strongman and retired general Hugo Banzer took a strong lead tonight in Bolivia's presidential elections, outdistancing his nearest rival more than two to one.

The voting was marred, however, by hundreds of complaints of voter fraud and election irregularities. In La Paz alone, scores of election boxes did not have padlocks as required by law, officials here said.

According to unofficial returns provided by Radio Fides, an independent Jesuit-run radio station, totals representing about 22 percent of the votes showed the right-wing Banzer with 41.1 percent.

Banzer's nearest competitor was twice-president and center-right hopeful Victor Paz Estenssoro, 77, who was running less strongly among Bolivia's large peasant population than his managers had hoped. Paz reportedly received 21.1 percent of the votes counted.

Political analysts here say the results may portend a radical shift in the political loyalties in this country of nearly 6 million people, as the left's once all-powerful electoral attractiveness appears to have nearly evaporated following 33 chaotic months of democratic rule under a center-left government.

Banzer, 59, ran this landlocked nation for seven years following a bloody coup in 1971. Although he was generally credited with having brought order to South America's most anarchic country, Banzer is also criticized for having outlawed strikes and repressed political opponents.

As suggested by recent polls, Banzer tonight appears to be wrapping up a large enough plurality to assure him victory. However, according to the Bolivian constitution, Congress must decide among the three top vote getters if no candidate receives an absolute majority.

Should Banzer's lead significantly shrink, former vice president Jaime Paz Zamora, 46, a center-left candidate, may hold the balance of power in the parliamentary vote, slated for Aug. 2. The Radio Fides survey showed Paz Zamora receiving 8.5 percent of the votes tallied.

However, political analysts said that if Banzer's margin holds it would be difficult for his opposition to deny the former military man his victory.

Voters were choosing a replacement for President Hernan Siles Suazo, who in 1982 became the first popularly elected president in nearly 20 years.

Despite some delays in openings of polling places, rumors of potential violence and the possibilities of massive fraud in the polling, a large, peaceful turnout was reported among the 2.1 million registered voters. Voting is mandatory and failure to comply can result in a fine.

"In the countryside, things are developing normally, although there have been scattered incidents reported in the La Paz area this afternoon," said Edgardo Valverda, a spokesman for the National Elections Commission.

The armed forces commander, Gen. Simon Sejas Tordoya, promised that the coup-prone military would respect the election results.