The brazen assault last week by a Colombian guerrilla movement on the country's Supreme Court building, and the government's unyielding response, marked the most serious setback to date for the shaky peace process pursued by President Belisario Betancur since he took office three years ago.

Out of the ashes of two days of savage warfare between M-19 guerrillas and Colombian security forces -- which gutted the concrete courthouse, left at least 85 corpses of magistrates, rebels, court employes, visitors, soldiers and police, and burned the remains of others -- Betancur hopes to salvage his peace plan. It has been one of the centerpieces of his Conservative government and was touted as a model for other Latin American conflicts.

But supporters and critics of the Colombian leader say the fierce battle in Bogota's government square is almost certain to mark a turning point in relations between officials and the country's various rebel groups, as well as intensify a national debate over how tough or conciliatory the government should be with the terrorists.

"I'm afraid this is going to divide the country," said Enrique Santos, editor of the capital's main daily, El Tiempo. "Those who had opposed the president's policy as being too lenient will now claim they were right, while others sympathetic to the guerrillas' cause and eager for domestic peace will push for a continuation of dialogue and agreement."

After an emergency Cabinet meeting Saturday, Justice Minister Enrique Parejo said that a special commission would investigate the siege, Reuter reported. The commission was set up after judges who survived the ordeal called for an investigation, saying the government should have heeded a cease-fire call by Supreme Court President Alfonso Reyes, who was among those killed.

Even before last week's explosive clash, Betancur's peace process appeared to be in serious trouble. The M-19 movement and the People's Liberation Army, which were two of the three main guerrilla groups to sign tentative pacts with Colombian authorities last year, had pulled out of the agreements. They complained of official foot dragging on adoption of political reforms and announced a return to open combat with the government.

The opposition Liberal Party, which holds a majority in Congress and has criticized Betancur's approach as ineffective, refused a presidential invitation to participate in the new committee.

"The government now is in a very bad situation," said Carlos Lemos, who was foreign minister in the Liberal government preceding Betancur's. "It has to realize the failure of its past policies. There is a feeling among some of us that the president himself is guilty of what happened last week, that the appearance of weakness of this government encouraged the guerrillas to think they were strong."

Several western diplomats here took a milder view. They saw the M-19 attack not as a show of strength but as an act of desperation by a weakened, poorly led band of rebels. To declare Betancur's peace process finished would be premature, they said.

Most encouraging for Betancur is the pact he still has with Colombia's largest and oldest guerrilla movement, the Colombian Revolutionary Armed Forces (known by the initials FARC), which accounts for about half the roughly 12,000 peasant insurgents believed to be operating in the country. FARC, thought to be the military arm of the pro-Moscow Colombian Communist Party, has formed its own political party -- the Patriotic Union Party -- which is scheduled to hold its first national congress in Bogota this month with an eye to next year's presidential elections.

But FARC's involvement in the peace process remains ambiguous. Alongside its calm official pose and political moves, its gun-toting members continue to carry out kidnapings and extortion.

Several senior government aides have been quoted in the local press as saying the peace process would have to be reassessed in light of this week's dramatic battle. Betancur himself, in a gesture suggesting that he realizes how politically delicate the situation has become, has announced his intention to consult closely with ex-presidents from the Liberal Party in days ahead.

Betancur's program of amnesty, dialogue with guerrilla leaders and offers of wide-ranging political and economic reforms represented a sharp departure from previous government policies of military repression that had failed to eliminate Colombia's five main guerrilla groups.

Despite setbacks and continued sporadic warfare, agreements were reached last year under which insurgents from three groups -- FARC, M-19 and the People's Liberation Army (an armed branch of the Maoist Communist Party) -- pledged to stop all terrorist actions and kidnapings, though the rebels were allowed to keep their arms. In exchange, the government signed a vaguely worded commitment to give the insurgents a role in effecting political and social changes.

Betancur was trying to follow the example of neighboring Venezuela, a democratic country that offered amnesty to its guerrilla insurgents in the late 1960s and eventually welcomed former guerrilla leaders as delegates in the national Congress. But Colombia is not Venezuela. In Venezuela, the guerrillas were decisively defeated in the field and joined an oil-rich society filled with economic opportunity. In Colombia, 28 million people remain handicapped by underdevelopment and traditionally strong barriers.

The Betancur government has spent $35 million in the past three years in job training programs and educational grants to help ex-guerrillas return to normal lives. About 50 taxicabs in Bogota, for instance, were bought with public funds and are now driven by former rebels.

Even so, the resources the government could draw on to aid surrendering insurgents were relatively scanty. Moreover, Betancur and the rebels had different conceptions of what the peace process was supposed to accomplish.

"The insurgents were looking for a way to fundamentally change the system, while the government was looking for a way to incorporate them back into society," explained a foreign diplomat. "For them, it was a stage in the revolution. For the government, it was a way of avoiding a revolution."

From the start, Colombian conservatives have opposed the peace effort, saying it rewarded terrorism. They have doubted that an elected government could negotiate a lasting peace with leftist guerrillas committed to its overthrow.

Some local Army officials, contemptuous of Betancur's amnesty decree, did not slacken efforts to fight guerrilla groups that agreed to a truce. Many Colombians have grown increasingly skeptical about the possibility of attaining a durable peace accord in the Andean republic. But Betancur has argued that more than 30 years of counterinsurgency in Colombia had failed to crush the rebels.

Left-wing guerrillas ambushed an Army patrol in the Andes Mountains in southwestern Colombia today, killing 10 or 11 soldiers, radio stations reported.

[Radio Todelar quoted military sources as saying members of three guerrilla organizations -- the M-19, the Ricardo Franco Brigade and the Quintin Lame -- joined forces in the ambush, The Associated Pres reported.]