BOGOTA, COLOMBIA, MAY 27 -- Cesar Gaviria Trujillo, the candidate of the ruling Liberal Party who vowed to step up efforts against drug traffickers, was elected president of Colombia today in voting that was peaceful despite threats of attacks by cocaine barons.

With 85 percent of the precincts reporting, Gaviria, 43, an economist who entered the race following the August assassination of Liberal candidate Luis Carlos Galan, was winning about 48 percent of the vote, leading his nearest rival by 22 percentage points. An absolute majority is not needed to win.

In his victory speech, delivered under tight security to several hundred cheering supporters, the president-elect warned that the international community must do more to help Colombia fight drug trafficking.

"I would like to make it clear to the international community that Colombia is paying a very high price -- the lives of our best men, our magistrates, judges and policemen -- and we do it in defense of our basic principles," Gaviria said. "We will defeat narco-terrorism. However, drug trafficking is a multilateral problem and industrialized countries are doing too little to stop consumption. . . . Rhetorical support and declarations that we are not to blame are not enough."

The three other major candidates acknowledged Gaviria's victory.

Alvaro Gomez was second with 25 percent. He is a former member of Colombia's second major traditional party, the Social Conservatives, who formed the Movement for National Salvation.

Running third was Antonio Navarro, an ex-commander of the M-19 guerrilla movement who helped negotiate a peace agreement that was implemented in March, with 12 percent. Rodrigo Lloreda, the official candidate of the Social Conservatives, was running fourth with about 11 percent.

The showing of the M-19 was the election's major surprise. It is the strongest showing ever by a leftist party in Colombia, and especially significant given that some 1,100 leftist politicians have been assassinated in the last four years. The M-19 had only two months to organize as a legal party after laying down its weapons and joining the political process.

"We are the political phenomenon of the 1990s, and we are beginning to change the history of Colombia," Navarro said at a press conference. "We are very pleased with the results, and are preparing to become the largest party in Colombia."

A spokesman for Gaviria, who won every department and 22 of the 23 departmental capitals, said that the candidate would address the nation later. He said Gaviria would invite both Gomez's movement and the M-19 to form part of his government, leading to a sharp realignment in Colombian politics. The Liberals and Social Conservatives have dominated the political structure for 50 years.

Gen. Oscar Botero, minister of defense, said the election was one of the most peaceful ever in Colombia, and added, "Democracy has completely defeated terrorism."

The election in South America's most enduring democracy was widely seen as a referendum on how to deal with drug trafficking and its associated terrorism, themes that dominated the campaign amid claims by politicians and others that the cocaine cartels were out to destroy the political system.

Three presidential candidates were killed in the last nine months, and a series of car bombs have been set off in the last two weeks in the nation's largest cities, leaving dozens dead and hundreds wounded. Authorities say the attacks were ordered by Pablo Escobar, leader of the Medellin cocaine cartel, in retaliation for the government's crackdown on the drug trade.

Gaviria has proposed stepping up the fight against drug traffickers by forming special courts to handle terrorism and continuing the extradition of suspected drug traffickers to the United States. Extradition is viewed by U.S. officials as crucial to fighting the traffickers because of the drug barons' ability to intimidate or kill Colombian judges.

Gaviria's three main opponents favored formulas for negotiating with the traffickers to end the violence, and all would immediately halt extradition, a topic that stirs deep nationalistic feelings here.

The four major candidates for the four-year presidency called on their followers to vote as a way of defeating terrorism, but voter turnout appeared to be below the normal at 46 percent. Voting is not obligatory here.

Thousands of troops patrolled the main cities, mixing with street vendors hawking food and souvenirs as voters danced and sang.

"I am not afraid. I am confident everything is under control," said an elderly woman lined up to vote at the International Fairgrounds, where a bomb-disposal unit was the chief attraction of passersby. "I hope nothing happens, because it will damage the entire process."

Voters also overwhelmingly approved a measure calling for an assembly to revise the nation's 19th century constitution. How the assembly would work has not yet been defined, but Gaviria said he would use the session to deal with the battered judiciary and reform the ineffective congress.

Senior police sources said the tranquility of the day was due to a series of raids in the capital that led to six arrests and the confiscation of 4.5 tons of dynamite and detonators intended for use in car bombs.