Representatives of the Columbian government met for the first time today with leftist guerrillas holding more than 40 hostages and the guerrillas then freed five more of their captives.

The initial negotiating session, lasting 90 minutes, was held in a police van parked outside the Dominican Republic's embassy that the guerrillas seized during a reception last Wednesday.

While the hostages include 14 ambassadors and numerous other diplomats, those released today were four waiters and a doctor. Including the women and wounded released earlier, 23 hostages have been freed.

Representing the government today were Camilo Jimenez Villalba and Romiro Zambrano, both high-ranking officials in the Foreign Ministry. They met with one of the guerrillas, her head covered by a white hood to prevent identification, and Mexican Ambassador Ricardo Galan, one of the envoys among the hostages.

Neither side gave details of the negotiations but the government and the guerrillas agreed to hold a second round, which is not expected to be held before Tuesday.

The Colombian government issued its 10th communmique since the crisis began, saying only that the M-19 guerrillas had formally presented their demands and that the government had expressed its desire to resolve the tense situation as quickly as possible and achieve the safe release of the hostages "with respect for the constitution and laws" of Colombia.

The guerrillas' principal demand is that 311 political prisoners, more than 200 of them members of the M-19, be freed from Colombian jails and flown out of the country in exchange for the remaining hostages, among them U.S. Ambassador Diego C. Asencio.

Jurists and government officials are debating whether President Julio Cesar Turbay Ayala could legally agree to release the prisoners, even if he decided he wanted to do so. The reference to this question in the communique appeared to signal determination to observe Colombia's laws at all costs.

It is believed that the M-19 commando force still holds about 40 hostages, among them the ambassadors of the Dominican Republic, the United States, Brazil, Mexico, Uruguay, Venezuela, Guatemala, Austria, Switzerland, El Savador, Haita, Egypt, Israel and the Vatican.

Frank Perez, the deputy director of the State Department's office to combat terrorism -- sent from washington shortly after the siege began -- said today that the guerrillas' decision to release more hostages "may indicate that the terrorist find it easier to maintain fewer . . . hostages [or] it could indicate that they're showing some flexibility."

About an hour before the negotiation began, police killed at least one occupant of a car that entered the zone surrounding the embassy, reportedly having ignored warnings to halt. It was not immediately clear if the car's occupants had any connection with the siege.

In a ceremonial prelude to the negotiations, apparently carried out according to guerilla demands, the parties to the talks stood at attention beside the police van while the occupants of the embassy sang the Colombian national anthem.

The Mexican ambassador is one of a team chosen by the captive envoys to represent them in dealing with the guerrillas and, as it turns out, the Colombian government as well.

[United Press International quoted the foreign minister of Bolivia as saying that Pope John Paul II would take part in efforts to free the hostages. The Vatican did not rule out such a role but would not confirm any such initiative.]

Perez, the antiterrorist expert, said the United States has not tried to influence the Colombian government's policies or conduct since the takeover other than to say "we would not want [it] to do anything precipitous to endanger the lives of the hostages."

"We don't give in to terrorist black-mail," Perez said, but he indicated that the United States would not necessarily expect the Colombian government to adopt such a rigid position. "In this case, we're looking to the Colombian government for the safe release of our ambassador."

Perez said believes the M-19 guerrillas are "a very disciplined terrorist group." He characterized the takeover as 'a' very well-planned operation" and said that he believes the "goal is to bring down the Colombian government."

The situation now, Perez said, appears to have stabilized somewhat and "the longer these things go on, the better the chance the hostages have of coming out alive" because of psychological affinities that develop between captors and hostages, making it more difficult to carry out death threats.

Perez said his role is to advise the U.S. Embassy on its dealing with the Colombian government and to report back to a special crisis task force in Washington.