Virgilio Barco Vargas, a U.S. engineering school graduate with a reputation as a forceful administrator, said today he would use his overwhelming presidential election victory to initiate "a process of change benefiting those less favored" and creating "a society more just, less unequal and more united."

With most of yesterday's ballots counted, Barco was winning by 1.6 million votes, the largest margin in Colombian history. Representing the Liberal Party, Barco received 58 percent of the vote to 36 percent for Conservative Alvaro Gomez Hurtado.

Barco's triumph was expected to help him realize an ambitious program of agrarian reform and economic revitalization, including more jobs and housing for the poor, projects which his predecessor, Conservative Belisario Betancur, had also promised but failed in large part to deliver.

"Barco could turn out to be the president Betancur tried to be," said a foreign diplomat, noting that the two men share many of the same center-left policy goals.

A strong Liberal Party showing in March congressional elections has assured Barco an ample majority in Congress, an advantage Betancur did not have.

One of the new president's top priorities will be to deal with Colombia's nagging guerrilla problem. Barco, who is to be inaugurated Aug. 7, has signaled plans to carry on the process of dialogue begun by Betancur, but under more defined conditions.

Barco is reportedly inclined to offer more precise guarantees of urban and agricultural changes advocated by the left. But he is considering demanding, in return, that the guerrillas surrender the arms Betancur let them keep under earlier cease-fire agreements.

Gomez, whose hard-line, belligerent image dogged him during the campaign, was defeated in a 1974 bid for the presidency by 1.3 million votes, the second largest margin in Colombian history.

Leftist candidate Jaime Pardo Leal, running under the banner of the Patriotic Union, a political movement formed last year by the Communist Party and the Revolutionary Armed Forces of Colombia -- the only guerrilla group still observing a cease-fire agreement -- drew 4.4 percent.

Regina Betancourt de Liska, who as the Metapolitical Movement candidate attempted to combine populism and mysticism, got less than 1 percent.

In addition Barco's solid congressional majority, also working in Barco's favor is an upturn in the economy, due to the rise in the world price of coffee -- Colombia's principal export -- and increased development of oil, coal and nickel reserves. Falling international interest rates are saving Colombia large amounts in its relatively modest foreign debt payments. The fiscal deficit has fallen from 6.2 percent of gross domestic product when Betancur assumed office four years ago to 2 percent this year.

Summing up these trends, the National Association of Industries said last week that current economic perspectives for Colombia are the best in 10 years.

In a written statement to the foreign press, Barco said: "I would like you to believe that Colombia will enter a process of change benefiting less favored sectors of the population. I would like you to believe that we are going to adopt some reforms to make our society more just, less unequal and more united."

Barco, who has served as ambassador in London and Washington and as a World Bank director, has said he will keep Colombia in the Nonaligned Movement and involved in the Contadora group of eight Latin America countries seeking a peace treaty in Central America. But he is known to be less inclined than Betancur to take an activist role in the Contadora process and more likely to concentrate on relations with immediate neighbors.

Although the issue of Colombia's drug trade was hardly addressed in the campaign, Barco has assured U.S. officials that he, like Betancur, will support eradication programs and cooperate with U.S. efforts to extradite Colombians charged with trafficking.

Many of the projects Barco is expected to launch are still in the planning stage. As the clear front-runner during the campaign, the Liberal leader spoke more in generalities than details -- a strategy that one senior adviser said had been adopted so as not to raise public expectations too high.

Barco's government will probably have a more partisan cast than recent Colombian administrations. The president-elect has signaled his intention to abandon the traditional practice of coalition rule between the two major parties, a carryover from the 1958 National Front power-sharing agreement that brought political peace after a decade of bloody civil war.

Conservative Party leaders have expressed a willingness to discuss with Barco the elimination of a constitutional clause mandating that an administration provide an "adequate and equitable" distribution of offices between the parties.

"Barco will bring a new breed of people into government," said Fernando Cepeda, a law professor and Liberal Party strategist. "By that I mean he will invite those not so involved in politics or government."

While apt to give fewer appointments to the opposition Conservatives, Barco said in the campaign he is prepared to appoint leftist Patriotic Union members as mayors in towns where the movement won a majority of council seats in March. The old lock on political power held by the two major parties is one of the factors often blamed for the propensity of young leftists to take up arms against the government.

Barco, 64, has served in numerous government posts -- although few of them elected -- since graduating in 1943 from the Massachusetts Institute of Technology with a degree in civil engineering.

As minister of public works, and later as minister of agriculture, he built a reputation as an able, performance-minded administrator. His tenure as mayor of Bogota in the late 1960s is credited with changing the face of the capital by adding roads, parks and schools. His slogan then -- "When it's time, it's time" -- contributed to his image as a hard-driving politician.

Described by friends as meticulous and analytical, Barco is said by an adviser to have studied last night's election returns on a computer in a hotel room.

Barco's U.S.-born wife Carolina has been active in charity work and the arts. They have four children.