CALI, COLOMBIA -- The cocaine cartel that takes its name from this city has become Colombia's largest, outstripping the more violent Medellin group, according to Colombian and international narcotics experts.

Precise figures are difficult to ascertain, but a little more than a year ago the Medellin cartel was believed to be responsible for about 75 percent of the cocaine shipments to the United States and Europe. Now, say officials, Medellin's share is below 50 percent.

The realignment is believed by authorities to be a major factor in sparking a bloody feud between the Medellin and Cali operations -- which for a decade have dominated shipments abroad, principally to the United States.

While Medellin cartel leader Pablo Escobar has been driven underground, Miguel and Gilberto Rodriguez Orejuela and Jose Santacruz Londono, suspected leaders of the Cali operation, recently were spotted at a party of the city's elite at the Intercontinental Hotel -- attended by at least one prominent senator and numerous local politicians -- said two sources here who attended.

Cali, with 1.2 million people, is an agricultural and industrial center with a wide mix of ethnic groups and cultures and has suffered little of the violence that has plagued the larger Medellin.

But on Sept. 25, a group of Escobar's hitmen gunned down 19 people on a farm outside Cali. Apparently the target was the farm's owner, Francisco Herrera, said by police to be a leading partner in the Cali syndicate. Herrera escaped injury.

The Rodriguez Orejuela brothers "know they can control the state, but not Pablo Escobar," said a source close to them. "Escobar is their number one enemy, and that is the group they fear, not the police."

President Cesar Gaviria has stated that stopping narco-terrorism, largely sponsored by Escobar, is the government's chief priority, and other senior government officials say they do not have the resources to wage the war on trafficking on all fronts simultaneously.

The result, according to narcotics experts, is that the Cali operation has flourished while the Medellin cartel has lost key people and had its distribution networks disrupted.

"The Medellin cartel has begun to lose some of its members, and at the same time the power it exercises over the world distribution network," said a recent Interpol report. "Its quota could now be as low as 40 percent after at one time having controlled up to 75 percent."

A U.S. narcotics expert here said that, while it was difficult to give an exact breakdown, "every day that goes by, the Cali people get a bigger cut of the market. My gut feeling is that the breakdown is at least 50-50, and Cali gains every day."

The hatred between Escobar and the Cali leaders is both personal and professional, according to sources in Cali and Bogota, and the latest conflict appears to have been sparked in part by the Cali group's growing share of the lucrative European market. European experts say the Medellin cartel has been muscled out of several distribution networks.

Colombian authorities say that in 1988, the two groups carried out a series of attacks against each other, and in 1989 the Cali syndicate hired a group of British mercenaries to kill Escobar. The mission failed when one of two helicopters involved crashed.

Because the Cali traffickers fear a violent response to Escobar's latest killings could prompt a crackdown against them, sources close to the leaders say, the Cali group has been passing intelligence on Escobar to authorities through third parties. Escobar has publicly accused the Cali group of cooperating with the authorities.

"The Cali people view the Medellin cartel as their biggest enemy, but do not want open war," said one source close to the Cali leadership. "They pass on information to help authorities deal with Medellin as a problem of public order."

Colombian and U.S. authorities say there is no knowing collaboration with the Cali cartel but admit they cannot check who is behind every informant. "We will not get into bed with one cartel to dismantle their opposition," said the U.S. expert. "That is unacceptable."

In at least one case, the Cali group has passed on intelligence to local authorities. Six days before the Sept. 25 massacre, the Rodriguez Orejuela brothers sent a signed letter to the mayor of Cali, German Villegas, warning that Escobar had moved men into the area.

"As is obvious, we have established intelligence organisms, purely for defensive reasons, which allow us to state without a doubt that there is a plan underway to destabilize the regional and municipal governments," said the letter, made public early this month, referring to "more than 20 people of that organization, with vehicles, dynamite and weapons . . . with a specific plan to attack prominent families here, as well as our families and businesses."

Authorities say there is increasing evidence that Escobar has forged an alliance with at least a faction of the Marxist-led National Liberation Army, paying the guerrillas to carry out kidnappings and assassinations.

"Something had to change for Escobar to be able to go back on the offensive," said the U.S. expert.

The personalities of the leaders of the two cartels are as different as their operating styles.

While Escobar got his start as a thief and hitman in the slums, Gilberto Rodriguez Orejuelo, from the middle class, is a banker known as "the chess player" for his love of the game and calculating style. His brother Miguel is a lawyer. Santacruz Londono is an engineer.

"They never challenged the political structure, they just bought it," said a law enforcement official. The Cali operation is less centralized than the one in Medellin, and sources in Cali say a group of mid-level traffickers operate in almost complete autonomy, coordinating with the leaders but seldom dealing directly with them.