BOGOTA, COLOMBIA -- "The Winds of War," read the cover of a leading Colombian magazine recently, foreseeing an end to the three-year truce between the government and the country's main guerrilla group.

Truces with smaller leftist rebel movements unraveled two years ago, pitching this violence-prone nation into a steady stream of almost daily casualty reports on Army-guerrilla clashes.

But as long as a cease-fire has remained nominally intact with the oldest and largest guerrilla organization -- the Moscow-line Revolutionary Armed Forces of Colombia, known as FARC -- politicians and rebels alike have been able to speak of a continuing "peace process."

Now that cornerstone accord appears to be crumbling. A FARC ambush last month of a convoy of Army road builders along a remote jungle highway in the southern province of Caqueta killed 27 soldiers and wounded 42 -- the highest military toll in 15 years.

What was shocking about the Caqueta attack was not just the death toll. Skirmishes between military patrols and FARC units had been occurring with some regularity, each side accusing the other of violating the truce. But the location of the assault took the government by surprise. Officials had considered Caqueta relatively calm.

The timing, too, was unexpected, coming just as campaigns are about to start for municipal elections next March. The vote will mark the first direct election of mayors in Colombia, and FARC -- through its political affiliate, the Patriotic Union -- stands to win in rural areas where the guerrillas hold sway.

According to a Cabinet member, President Virgilio Barco's initial impulse after the ambush was to abrogate the truce and turn security forces loose on the communist rebels. But Barco reconsidered and, in a televised address declared that the cease-fire would be considered broken only in regions, such as Caqueta, where FARC units attack government troops.

Given the high incidence of Army-guerrilla clashes around Colombia, Barco's formula seemed certain to nullify the fragile cease-fire in numerous parts of the country. Some analysts said the military, which has never been enthusiastic about the peace process, would now have more reason than ever to provoke confrontations with rebel groups.

One foreign diplomat who has followed the guerrilla problem closely predicted the cease-fire would completely dissolve within the next few months. "No one wants to be seen as being responsible for breaking the peace process," the diplomat said. "But the recent attack has given the process another big push toward collapse."

Even so, a major factor holding together the bare threads of an accord is the recognition that neither the government nor FARC could win a civil war. Both sides have used the truce to strengthen their forces. Although the Army still outnumbers FARC's roughly 10,000 members six-to-one, the guerrillas would have an advantage over conventional forces in the rugged mountain and jungle terrain where most battles would be fought.

Barco's predecessor, populist Belisario Betancur, initiated formal talks with Colombia's handful of rebel groups. Elected president in 1982, Betancur raised national hopes that negotiations could end leftist insurgencies that decades of intermittant military drives had failed to repress.

Betancur demonstrated his good faith by granting an amnesty to imprisoned guerrillas. Two years later, the government signed cease-fires with the most prominent guerrilla organizations. But promises of increased social spending and structural reforms, which would expand Colombia's oligarchic ruling circle, were slow in coming.

By mid-1985, some guerrillas had grown tired of waiting. Both the nationalist April 19 Movement (M-19) and the pro-Cuban National Liberation Army renounced the truces. In November 1985, security forces stormed the Palace of Justice after M-19 commandos seized hostages inside. More than 100 people died, including nearly half of the justices of the Supreme Court.

Since stepping into the presidency last August, Barco has sought to sustain the hope of peace. But he has said less about negotiations and more about a $1 billion "rehabilitation plan" that aims at undercutting support for the rebels.

Spread over 35 percent of the nation's territory and 10 percent of the population, the program is meant to reduce poverty and counteract a widespread sense of alienation from legitimate authority.

Few projects have materialized. Most communities are still forming "rehabilitation committees" to draw up local wish lists for new roads, clinics and schools.

FARC leaders, moreover, have been upset by Barco's elimination of special independent commissions established by Betancur outside official ministries to monitor and mediate government-guerrilla disputes. Intent on institutionalizing the peace process, Barco has designated a senior aide, Carlos Ossa, to manage guerrilla affairs.

Ossa has traveled three times to FARC's mountain-top headquarters at La Uribe near Bogota. The government and rebels regularly exchange messages on a "hotline" radio link.

But FARC chiefs continue to demand a "verification committee" as a forum for airing accusations of truce violations. In a statement after the Caqueta attack, FARC's high command suggested that the ambush would not have happened had such a committee existed.

Ossa described the June 16 assault as an "act of desperation" intended to recover the rebels' lost initiative. Other government officials speculated that the rebels may have attacked in order to guard against planned eradication of coca plantations in Caqueta. FARC is said to levy taxes on coca receipts in areas the movement controls.