BOGOTA, Colombia (AP) — Absent from the peace talks opening in Norway this week between Colombia’s main leftist rebel movement and the government will be the guerrilla heavyweights who presided a decade ago over the last attempt to end a conflict that has claimed tens of thousands of lives over nearly half a century.

Either they are dead, mostly killed in military raids, or believed to be in the field commanding an insurgency badly battered by a Colombian military fortified by years of U.S. financial and logistical support.

This time, most of the faces and names of the negotiators for the Revolutionary Armed Forces of Colombia, or FARC, are little known to their countrymen. And unlike in the last talks in 1999-2002, the rebels this time enjoy no safe haven. President Juan Manuel Santos would not agree to one.

Both parties to the negotiations were keeping a low profile heading into the talks at an undisclosed location outside Oslo. There is no media access and even the hour and date of the first meeting are uncertain, though a news conference is set for Wednesday.

The rebels, meanwhile, have offered only a vague sense of what they will demand in exchange for laying down their arms, beyond land reform and guarantees of safety for fighters who demobilize.

On Sunday, about 200 people rallied in central Bogota to demand an accounting from the FARC for relatives kidnapped by the rebels and never released.

Andres Pastrana, who presided over Colombia’s last round of peace talks that ran nearly the entire length of his 1998-2002 presidency before collapsing in discord, is among Colombians who wonder why two still-powerful commanders who took part in the previous negotiations, Joaquin Gomez and Fabian Ramirez, will be absent from the Norway talks.

‘‘The question we have to ask is: Is the FARC monolithically united behind this process?’’ said Pastrana, who met secretly with legendary FARC founder Manuel Marulanda in 1998 to arrange the last round of talks. ‘‘I don’t have that very clear. Let’s hope it is.’’

The FARC negotiators, whose discussions with the government are to move to Havana later this month, include one member of the rebels’ ruling six-man Secretariat, Ivan Marquez, as well as Marco Leon Calarca, the rebels’ public voice during the 1990s.

Another negotiator, Ricardo Tellez or Rodrigo Granda, was seized in 2004 by Colombian agents in Venezuela but freed by the Colombian government three years later as a good-faith gesture to encourage the FARC to free all its ‘‘political hostages.’’

The rebels released their last such captives in April, meeting a condition of the agreement under which secret preliminary talks began on Feb. 23 in Havana.

The only top FARC negotiator well-known to Colombians, Ricardo Palmera, is serving a 60-year sentence in the United States. A former banker, he gained fame during the last talks.

Colombia’s chief prosecutor has said that Palmera could be allowed to participate in the Oslo talks via teleconference from a prison in Colorado.

Palmera was convicted in the abduction of three U.S. military contractors whose surveillance plane crashed in rebel territory in 2003 due to mechanical failure. The three men were rescued in July 2008 along with former presidential candidate Ingrid Betancourt in a sophisticated ruse involving Colombian commandos posing as international relief workers.

Many of the FARC’s former top leaders have been killed by the military in raids that began tipping the conflict in the government’s favor in 2008.

Marulanda died of an apparent heart attack in 2008 just after its chief spokesman at those talks, Raul Reyes, was killed in a cross-border military raid into Ecuador that briefly brought regional tensions to a boiling point. In September 2010, the group lost its undisputed field marshal, Jorge Briceno, or Mono Jojoy, in an air assault on his jungle hideout. And Marulanda’s successor atop the FARC, Alfonso Cano, was killed by Colombia’s military last year.

The rebels’ footprint is also much diminished, though the insurgents have stepped up hit-and-run attacks in recent months, particularly on oil installations.