Surviving judges of last week's guerrilla assault on Colombia's Palace of Justice and most relatives of slain Supreme Court justices boycotted a memorial Roman Catholic mass called today by the government, reflecting mounting public protest against its handling of the emergency.

In an address at the end of the service, President Belisario Betancur acknowledged the criticism but said the results ultimately would strengthen the democratic rule of law in Colombia. "The choice is between democracy and terrorism, between law and lawlessness, between liberty and fear," said the 62-year-old Conservative president.

The decision to rush heavily armed government troops into the rebel-occupied courthouse within hours of its seizure has provoked protests from the legal community, university students and many poorer Colombians sympathetic to the leftist guerrillas' cause.

These outcries have shattered the initial appearance of national solidarity behind Betancur after the two-day siege ended Thursday with the deaths of 60 to 70 hostages or bystanders as well as 30 to 40 members of the M19 movement that seized the palace.

Betancur's management of the emergency also has been questioned by his Liberal predecessor, Julio Cesar Turbay, who headed the country when M19 rebels seized the Dominican Republic's embassy here in 1980 with a dozen foreign ambassadors inside. Turbay told reporters that during last week's conflict he had advised the president to take time to search for a peaceful solution.

After today's mass, in an impromptu encounter with reporters on the steps of the presidential mansion, Justice Minister Enrique Parejo said the government had tried to talk to the guerrillas after they seized the court Wednesday morning, but ordered the building stormed after becoming convinced that they did not want a dialogue and intended to kill the judges whom they were holding hostage.

The minister also said, however, that some aspects of the 28-hour siege remain unclear and that the entire episode would be the subject of an investigation by a special commission, ordered yesterday by the Cabinet. He added that surviving Supreme Court members would be invited to serve on the commission.

Meanwhile, the Ministry of Defense reported that M19 insurgents joined with two other small rebel groups yesterday to attack a military post in the southwestern province of Cauca, killing 11 Army soldiers and wounding another 11. The raid indicated that the guerrilla movement, although weakened by the loss of several leaders last week, has not been put out of action.

The mass in Bogota's cathedral was held with a large military honor guard and attended by senior members of the government, the armed forces and the foreign diplomatic corps. The boycott was to protest what the surviving judges maintained was the government's refusal to talk to the terrorists, but also to an alleged lessening of security at the Palace of Justice shortly before the guerrillas struck.

The only relatives of the dead justices to join in the televised service were the widow of Alfonso Patino Rosselli and her sister. The cathedral is on the same central square as the gutted Palace of Justice.

Surviving magistrates also rejected a government offer to receive special honors and told administration officials they were not welcome at burial services for the judges, held this weekend at various churches.

A court member, Humberto Murcia, has said the government discovered plans a month ago for the M19 attack, warned the justices and bolstered security measures at the courthouse, then relaxed those precautions last week. Murcia was one of only two Supreme Court justices who had been caught in the palace who survived.

Eleven of the court's 24 judges lost their lives in the fight, whether in cross fire, executed by the guerrillas or consumed by the fire that ravaged most of the five-story concrete courthouse. A 12th judge not in the building died of heart failure the day of the attack.

Asked about security at the Palace of Justice, Parejo said he had been assured by the Army and the police that it had been adequate. He disclosed, however, that a leader of the guerrilla force -- Andres Almarales -- had entered the courthouse two hours before the attack, dressed in civilian clothes and using an identity card issued in his own name as an attorney.

Parejo said he did not know if Almarales, who had benefited from a government amnesty, subsequently left the building or stayed until the arrival of the rest of his commandos -- who entered, disguised as police officers, in a van through an underground garage.

Since the end of the fighting Thursday, government officials have provided incomplete answers to a number of questions about the events that led to the storming of the palace. Many Colombians still have difficulty understanding why Betancur, who made negotiations with insurgent groups a centerpiece of his three-year-old administration, appeared hardly to pause before turning the military loose on the M19 guerrillas and their hostages.

Leaving the cathedral to scattered applause, the president stood on its steps, flanked by the minister of defense and the commander of the Air Force, as a military band played a martial-sounding hymn.

Then Betancur led a group of Cabinet members and military officers, walking two blocks to the presidential mansion along a route lined with presidential guards.

Explaining the government's moves last week, Parejo told reporters that the intention had been to keep military pressure on the guerrillas while offering them safe passage out of the courthouse and a fair trial. "We were looking for a way to free the judges while also trying to establish a dialogue," the justice minister said. "If we had stopped the operation, we thought it would have facilitated the takeover of key points in the palace by the guerrillas."