Mounting returns from Colombia's Sunday presidential primary indicated victory by a wide margin for former foreign minister Julio Cesar Turbay, who as Liberal Party candidate is expected to win easily in the June election.

Colombia, one of the few South American nations still to hold elections, carried out this one with a carnival atmosphere and only minor reports of violence. It was actually a final election for the national congress and municipal government at the same time that it served as the Liberal s' primary.

As expected, the Liberals outpolled the their traditional rivals, the Conservative Party, by a 5-3 margin in the voting for congress. Both parties were divided, as was the left, whose splintered parties made a weak showing.

Only about 30 percent of the 12 million eligible voters went to the polls, reflecting in part a crisis of confidence in the democratic system - which is beset by corruption and economic troubles despite record prices for the main export, coffee. With a population of 26 million Colombia is second in size only to Brazil on the southern continent.

The high abstention rate partly reflected a pattern for mid tern elections in past years, when Colombian voters have been particularly apathetic. But lack of clear issues this time, and a plethora of candidates, reinforced the tendency.

The main race was between Turbay, a former ambassador to Washington, and former President Carlos Lleras Restrepo for the Liberal Party nomination. Turbay will now face former labor minister Belisario Betancur, already chosen by Conservative Party, in the Presidential election.

Turbay, 62, controls the Liberal Party machinery and is generally considered one of the most astute politicians among the relatively few families that dominate politics here.

Because Liberals hold a heavy magin over Conservatives, he should win the presidency easily. There is a possibility however, that many of the Lleras voters among the Liberals could shift of Betancur in June.

Under a 16-year agreement between the two main parties, Liberals and Conservatives automatically alternated in the presidency between 1958 and 1974. Known as the National front, the agreement was the outcome of a civil war between the two parties that cost over 100,000 lives in the 1950s in what was called "La Violencia."

While ending the bloodshed, the National Front also tended to blur political differences between the two parties.

President Alfonso Lopez Michelsen, Liberal, was elected president in 1974 in landslide victory however. This was less because of his Liberal affiliation than the popularly held belief that would undertake social and economic reforms, but he failed to bring inflation or the rising crime wave under control.

Neither Lleras, Turbay, nor Betancur addressed themselves to the gut issues affecting the majority of the population during the congressional campaign, which a Colombian journalist described as a "polite match in name-calling."

Indeed, the differences between Lleras and Turbay were essentially over economic influence. Lleras represents the interests of the large landowners and industrialist. Turbay is close to the financial institutions, including the banks. Some of his followers, particularly on the Carribbean coast, allegedly are connected with Colombia's flourishing contraband and drug trade.

With little of political substance at issue, many poorer Colombiams opted to vote for the candidate that paid the most for their votes. There were charges of fraud in almost every region.

As one Colombian peasant woman said in explaining why she was selling her vote, "We don't get anything between elections so we might as well take advantage of the situation to get some land or food now. It won't make any diference to us who is president."