BOGOTA, COLOMBIA, FEB. 5 -- A 70-member assembly that is to rewrite the Colombian constitution began five months of deliberations today, with powerful drug traffickers pushing for a ban on extradition and for an amnesty.

The assembly begins meeting as powerful political sectors for the first time are criticizing President Cesar Gaviria's accommodation of the traffickers and perceived concessions after their latest crimes -- including the assassination of two of five hostages being held in a bid for more concessions.

The assembly was conceived not as a forum for drug issues but as a way to modernize the state and broaden political participation, including legitimization of leftist guerrillas if they demobilized.

Of Colombia's four main guerrilla forces, the M-19 laid down its arms last year, and had 19 representatives elected to the assembly. The Popular Liberation Army signed a peace agreement and is to demobilize March 1 and be given two seats in the assembly, raising the total to 72. Two other large groups continue to fight, and today they carried out about 50 attacks, killing about 45 policemen or soldiers, to protest their exclusion.

Drug trafficking and associated terrorism are expected to take up much of the assembly's debate. On Monday, the Medellin cocaine cartel's armed branch, which has dubbed itself the Extraditables and which claims to be a political-military organization, "respectfully requested" that the assembly pass a series of measures, including a ban on extradition. The traffickers seek to avoid extradition to face drug charges in U.S. courts.

Referring to the amnesty given to the leftist guerrillas, the Extraditables said that "other citizens have received pardons for the same crimes" that the traffickers have committed, and requested a commission "to hear our proposals."

Most commentators expect that extradition will be banned, and independent analysts say that if the assembly names a peace commission to talk with the guerrillas still fighting, it will likely do the same with the Extraditables.

What the assembly may do clearly worries the United States. Ambassador Thomas McNamara said in a recent press conference it would be a "grave mistake" for the assembly to ban extradition, although he acknowledged it was likely to happen, and he said an amnesty, while "unlikely," would be a "grave error and a disgrace to Colombia."

Carlos Lemos, a prominent member of the ruling Liberal Party and one of the assembly's few outspoken supporters of extradition, proposed not to debate any drug-related topics until all hostages were freed. But no agreement was reached.

"When someone has a gun to your chest, it is a monologue, not a dialogue," Lemos said. "You cannot deliberate freely if something you say can get another person killed."

The hope that Gaviria's policy of promising traffickers who surrendered no extradition and reduced sentences would keep narcotics issues from dominating the assembly has faded since two of the Extraditables' hostages were killed two weeks ago.

Diana Turbay, a magazine publisher and daughter of former president Julio Cesar Turbay, apparently was killed by traffickers during a Jan. 25 police raid of the property where she was being held. Marina Montoya, the 65-year-old sister of Colombia's ambassador to Canada, was shot six times in the face and head on Jan. 24. Her body was not identified until Jan. 31.

After Turbay's death, Gaviria not only promised to maintain his policy of plea bargaining with traffickers who surrendered, but announced that the benefits of the decree would be extended to crimes committed up to the date the trafficker surrendered.

Previously, the benefits only applied to crimes committed up to Sept. 5, 1990, the day the decree was issued. The change, demanded by the traffickers, means the Extraditables can escape full punishment for the kidnappings and the deaths of the two hostages and of two drivers that occurred during the abductions.

But the brutality of the Montoya murder galvanized those who felt the government was giving away too much, and brought the first widespread, public criticism of Gaviria's policies.

"From what we can see, the narcos are winning," wrote Antonio Caballero, a prominent columnist in El Espectador newspaper.