BOGOTA, COLOMBIA, AUG. 16 -- The gunmen who assassinated a leading presidential candidate a year ago, sparking a government war against the Medellin cocaine cartel, were trained by an Israeli mercenary, a senior police official said here today.

Gen. Miguel Maza Marquez, the director of the Department of Administrative Security, the equivalent of the FBI, said in an interview that in the year since the war was launched the Colombian government has made great strides in dismantling the cartel network that allegedly employed the mercenary.

Maza said new intelligence allowed him to make the first public link between the group that killed Luis Carlos Galan last Aug. 18 and retired Israeli lieutenant colonel Yair Klein, who is wanted in Colombia for training cartel gunmen and is suspected of providing them with sophisticated arms.

While cartel leader Pablo Escobar has not been captured or killed, Colombian and U.S. authorities say his trafficking and terrorist networks have been badly damaged by the government's strategy of tackling the traffickers head on.

"Today, we see a different country," said Maza, who has survived two assassination attempts. "A year ago our institutions, including the presidency, were endangered; now they are recuperating. The cartel had people infiltrated at every level, and that is diminishing. People who once viewed the traffickers with sympathy now give them no political space."

Despite Maza's largely upbeat assessment, the Galan case illustrates the difficulties the nation's judicial system still faces. A year after the crime, seven men are under arrest but have not been tried, and the key witness was killed last week.

Most of the state's case rested on the testimony of Jose Orlando Chavez Fajardo, a captured gunman who testified in exchange for immunity from prosecution. But after testifying, Chavez was allowed to go free without protection. He was killed Aug. 6, and the police report says the cartel paid assassins $60,000 to kill the star witness.

Maza said training by British, South African and Israeli mercenaries, especially by Klein, had given the cartel much of its ability to carry out terrorist attacks.

"Before they came, the cartel did not use car bombs; they did not have the capacity for indiscriminate terror," Maza said. "That colonel {Klein} taught them how to make bombs and did us tremendous damage.

"We have now linked Klein to the killing of Luis Carlos Galan," said Maza. "We can not arrest him {Klein} for participating in the crime because he was not in Colombia at the time, but we now want him for conspiring to commit the crime.

"Klein worked for {slain cartel leader Gonzalo Rodriguez Gacha} and trained his special forces," Maza said. "Among the students of Klein were those that carried out the killing. We have no doubt now that they were trained by Klein."

Klein, a private security specialist who acknowledges working in Colombia in 1988 and 1989, says he was working with cattlemen to teach them to defend themselves against Marxist guerrillas. He has said repeatedly that he did not work with drug traffickers.

Last month, Israeli police recommended that Klein be prosecuted for his role in an attempt to establish a military tactics school on the isand of Antigua, because clearance was not obtained from the Israeli government -- an offense punishable by three years in prison.

Last August, the government responded to the killing of Galan with an unprecedented crackdown, including the renewal of extradition of suspected drug traffickers to face charges in the United States and the seizure of huge tracts of land, luxury apartments, millions of dollars in cash, gold bars and jewelry and several hundred airplanes belonging to suspected traffickers.

Since then, more than 300 policemen, two other presidential candidates, hundreds of civilians, a senator, a half-dozen judges and three investigative reporters have been killed by the cartel.

The Galan assassination, which is being commemorated here in a week-long homage to the slain leader, also pushed the United States into expanding its role in the drug war. In addition to an emergency grant of $65 million in military assistance, the Bush administration raised its aid outlay from $22.8 million in fiscal 1989 to a proposed $135 million in fiscal 1991.

President Cesar Gaviria, who took office Aug. 7, was Galan's campaign manager and entered the presidential race after Galan was killed, promising to press the fight against drug terrorism and carry out the judicial and economic reforms Galan had campaigned for.

Among the biggest successes in the war on the cartel, according to Maza and other senior Colombian and U.S. officials, are the killing of Rodriguez Gacha in December and the killing last week of Gustavo de Jesus Gaviria, cousin and business manager of cartel leader Pablo Escobar.

One U.S. official said overall cocaine production in Colombia had fallen by about 20 percent in the last year. But officials acknowledge that the smaller, less violent Cali cartel has remained almost untouched in the last year and has been working with some success to expand while the Medellin cartel struggles.

"The Cali cartel has been hit but not in the same way," said the U.S. official. "The Cali people are now running from mansion to mansion, while Pablo Escobar is running from hut to hut."