Traffickers Threaten Land Reform. Drug lords are buying up land the government wants to redistribute to rural peasants. COLLISION COURSE IN COLOMBIA

CARLOS Ossa is a youthful and popular politician, but his new job puts not only his promising career but his life on the line. A rising star in the ruling Liberal Party, Mr. Ossa ran for mayor of Bogot'a last year and came in third.

Now he has taken over the top spot at the national land reform agency. This comes just when the government is launching an aggressive effort to break up large farms and distribute the land to poor peasants.

That puts Ossa and his Colombian Institute of Agrarian Reform (Incora) on a collision course with the country's violent drug traffickers.

Colombian traffickers have been buying up rural real estate and concentrating it in huge cattle ranches. Buying land provides the traffickers with a place to put their money and with physical security, say sources who follow the drug traffickers operations.

The phenomenon is so widespread that the Army's main drug fighter, Gen. Jaime Ruiz Barrera, has coined a term for the new landed gentry - ``narco-cattlemen.''

According to the respected newsweekly Semana, which based a recent five-page report on government statistics, the drug mafia has snapped up some 2.5 million acres (out of Colombia's 439,734 square miles) in the last five years.

``What's going to happen when Incora decides to take over the great estates of a drug trafficker?'' the Semana report asks.

Mr. Ossa says he doesn't know, but that he's determined to press on nonetheless. ``I'm committed,'' he says in an interview held in his office.

Ossa doesn't shy away from tough jobs. Until he resigned to run for office he was the government's negotiator with Colombia's five leftist guerrilla groups.

Now he bargains with large landowners.

Legislators passed a new agrarian reform law in late 1987 after a bitter battle that culminated in flying fists on the floor of Congress.

The law gives the government, for the first time, the power to force landowners to sell their holdings to Incora. The agency then resells the land to peasants under favorable terms.

A budget crisis put the plan on hold for most of 1988. Now Incora has its money, and Ossa is gearing up to buy 350,000 acres and distribute them to 5,600 families this year.

``This year is key,'' Ossa says.

Colombia has had an agrarian reform law on the books since 1961, but landowners managed to find enough legal loopholes attached to make the law ineffective. Most of the land bought by Incora was small farms, leaving the vast haciendas untouched. ``That wasn't land reform,'' Ossa says.

The failure of land reform preserved the highly skewed pattern of land distribution in Colombia.

A recent Incora report says that in a 27,000 square-mile-area, 54 percent of the land is concentrated in just 5 percent of the farms.

The concentration of land in hands of a few condemns the rest to a struggle for survival. Half of the families in zones which Incora says need reform cannot afford to buy basic necessities and thus fall below the government's ``absolute poverty'' line.

President Virgilio Barco came to power two-and-a-half years ago on a pledge to eliminate ``absolute poverty.'' But he has been unable to build much public support for this or any other major government initiative.

In fact, the President is considered so ineffectual that last June the country's leading business organization, known by the Spanish acronym Andi, urged him to resign.

A successful agrarian reform could boost Mr. Barco's low leadership rating. But as the government moves aggressively into the countryside it confronts the drug traffickers who got there first.

Analysts differ on how many drug dollars the traffickers bring back into Colombia every year. Estimates range from $500,000 to $3 billion. But there is one thing everyone agrees on - the narcos are putting a lot of their earnings into real estate.

The head of the national real estate organization, Oscar Borrero, says traffickers bought $5.5 billion worth of urban and rural property from 1979 to 1988.

In the countryside, the narcos' farms can be identified by their well-maintained fences and their ostentatious entryways.

The most famous of these belongs to top trafficker Pablo Escobar. His Hacienda Napoli is entered under an arch that holds an actual small plane said to have carried his first drug shipment to the United States.

Alonzo Berrio, an agricultural economist at the National University in Medell'in, the capital of the Colombian drug trade, says traffickers put their money into farms because real estate is an uncomplicated business to enter for a rising new rich class, unskilled in industrial investments and without access to Medell'in's closed commercial class.

``The recently arrived aren't easily accepted by this bourgeoisie,'' Mr. Berrio says.

There are other reasons why the narcos set themselves up in the remote countryside. One obvious attraction is physical security.

The rolling hills of a cattle ranch offer good escape routes. Although General Ruiz has a reputation as a tenacious enemy of the drug lords, he has captured no top traffickers since he was sent to Medell'in last year to crack the power of the cocaine kings.

On one raid in February 1988, the Army found an underground bunker and tunnel system buried on a farm outside Medell'in, but the traffickers had fled.

Remote ranches can hide not only traffickers but drug laboratories and the clandestine airstrips used to fly out the finished product. In June, General Ruiz's raiders discovered four labs, 2,600 kilos of cocaine, and three airstrips on one of Escobar's ranches on the west bank of the Magdalena River, not far from Hacienda Napoli.

The middle section of the long Magdalena River Valley has become a flourishing center for what the Semana article called ``Narco-Agro.'' In the middle of the valley, the traffickers' rural presence has taken on violent political overtones that could pose serious problems for Ossa and his agrarian reform effort.

Two of the most fanatically anticommunist cocaine kings, Gonzalo Rodr'iguez Gacha and Fidel Castano, have built up large cattle ranches in the area, according to government prosecutors.

Prosecutors say Mr. Castano and Mr. Rodr'iguez Gacha are using their ranches as training camps for paramilitary groups which the traffickers deploy against villagers who sympathize with guerrillas and leftists.

According to court documents summarized in the press, the government believes these paramilitary groups are responsible for massacres which took hundreds of lives in Colombia last year.

Rodr'iguez Gacha has large farms around the town of La Dorada, an area which Incora has targeted for agrarian reform. Other regions with large narco farms, such as the departments of C'ordoba, Antioqu'ia, are also slated for land redistribution by the agency. There were several massacres in these departments last year.

Ossa says he knows the traffickers are dangerous, but Incora will not treat traffickers with kid gloves. ``For us they're just another group of large landowners.''