BOGOTA, COLOMBIA, MAY 28 -- Cesar Gaviria Trujillo, at 43 the youngest person elected president of Colombia in this century, promises a sharp change in style from President Virgilio Barco, a fellow Liberal Party member.

"Politics is as important as policies," said one of his top advisers. "Barco has often let events overtake him. Gaviria is a good politician, and will shape events, not react to them."

Gaviria (pronounced Gah-VEER-ee-ah) won 48 percent of the vote on Sunday, beating his nearest rival by 23 percentage points. A product of the small political elite in Colombia's rich coffee growing area, the onetime economist promises a renovation and greater democratization.

A machine politician, Gaviria led the fight to weaken the party machinery. A pragmatist and seeker of compromise, he proposes no concessions in the war against narcotics traffic, which took the lives of three presidential candidates.

His support of extradition of suspected drug traffickers has made him the prime target of traffickers' gunmen. While the atmosphere in his heavily guarded office is tense, he laughed easily and spoke with emotion on Colombia's bleak situation in an interview last week.

"Colombia is facing perhaps the most powerful criminal organizations that have ever been faced," Gaviria said. "I do not think any country in the world has had to face criminal organizations with billions of dollars at their disposal. Our weaknesses have been exposed. We . . . need the tools to be able to face terrorism and defeat it."

Gaviria, as many Colombians, draws a sharp distinction between drug trafficking, viewed as an international problem, and the associated terrorism, which he said is Colombia's responsibility to fight.

In the interview and in his victory speech Sunday night, Gaviria accused the United States and other industrialized nations of doing little to battle drug consumption and of hindering Colombia's economic growth by closing its markets to legitimate products.

"We demand effective measures to reduce consumption," Gaviria said. "How . . . is up to them. If they fail, the tremendous effort being carried out by Colombia, and our great sacrifices will be lost in the face of rising demand."

But Gaviria's ability to continue to wage an all-out anti-drug war may depend on his ability to maintain fragmented public support for his program. Without an absolute majority, he does not have as clear a mandate as he sought.

"Gaviria will be as strong or stronger than Barco against the traffickers, as long as it is politically viable," said Luis Fernando Jaramillo, his campaign manager. "But if we do not see results, it will be difficult to maintain."

Gaviria said extradition should not be the main tool to fight traffickers and called for profound judicial reforms.

"We are in this situation because of the ability of the criminal organizations to kill or intimidate any judge in the country who interferes with their interests," Gaviria said. "We need to build a special judicial jurisdiction that has the capacity to face the fight against terrorism and drug trafficking." He proposes the formation of special tribunals of anonymous judges, high-security prisons and a code to force drug suspects to prove their money was gotten legitimately.

Those who know Gaviria well say he is a loner, has a short temper, and is calculating and self-confident. He was an outstanding student at Los Andes University, and a lover of rock music. His aides say his favorite English-language publication is Rolling Stone and his favorite band is Pink Floyd.

Gaviria rose rapidly through the Liberal Party and has surrounded himself with a corps of young advisers. Unlike most Colombian politicians, who are given to rhetorical flourishes, Gaviria is plain-spoken and direct.

At 27 he served as mayor of his home city of Pereira, then several terms as national representative. Gaviria joined Barco's cabinet in 1986, first as minister of finance, then as the powerful interior minister, where he earned the hatred of the far right with the first official denunciations of right-wing paramilitary death squads in rural areas financed by the drug barons.

Last year he took the politically risky step of agreeing to become left-leaning presidential candidate Luis Carlos Galan's campaign manager. Gaviria, who came out of the party establishment, was Galan's bridge to the party traditionalists. When traffickers assassinated Galan last August, Gaviria became the candidate to replace him.

Gaviria never forgot he was Galan's heir, and his campaign poster showed the candidate raising his arms in front of a face of Galan. He swept to victory in the March 11 primary, winning control of the party.