This country's landmark effort to pacify its powerful guerrilla armies, laden since its inception with improvisation and political brinkmanship, seems headed once again toward a time of crisis.

The government of President Belisario Betancur managed to conclude cease-fires last year with four of the five major guerrilla groups, halting the military activities of nearly 13,000 insurgents and offering the prospect of security to rural areas for the first time in nearly 40 years.

Yet in the past three months, little in this most ambitious of Latin American peace programs has seemed to go right. Army units have engaged in two tense standoffs with armed camps of the M19 organization since December, and in one case a major battle erupted before a settlement could be arranged.

In Bogota, an elaborately staged "national dialogue" to discuss proposals for peaceful reforms has all but broken down, abandoned by much of the country's political establishment. Guerrilla spokesmen have rejected suggestions that they surrender still considerable arsenals of weapons, and Congress appears reluctant to approve legislation meant to make room for the insurgents in the currently constricted political party system.

After 30 months of tortuous advances, breakdowns and marathon negotiations, many Colombians seem impatient with the peace process. "It was known that the road to peace would not be a comfortable highway," wrote columnist Enrique Santos Calderon recently in the leading newspaper, El Tiempo. "But few people imagined that it would become such an arduous and accident-prone stretch, filled at every turn with fatal traps."

At the same time, however, even Betancur's most ardent opponents are beginning to concede that the negotiation of peace in this country of 28 million people has already survived far more crises than most of the country's leaders had predicted it could.

Time after time during the last two years, the government's program seemingly was swamped by difficulties and was labeled a failure by both left and right. In each case, however, Betancur and guerrilla leaders have somehow talked themselves back from the brink of war and advanced just enough to ensure the process' survival.

"The end result has been a series of triumphs," said John Agudelo, the president of the government's peace commission. "It's just that Colombians have trouble recognizing that peace can really come after all these years. Lots of people had patience for the war but don't have any patience for peace."

Both government and guerrilla spokesmen now proudly point to several major achievements in the peace project. Following the passage by Congress of an amnesty in 1982 and the signing of truces with the major guerrilla groups last year, combat in the countryside has virtually ceased and farmers have begun returning to areas long known as free-fire zones.

Although urban kidnaping and extortion -- called "a national industry" by Agudelo -- continue at a high rate, guerrilla groups have renounced such activity and even publicly denounced dissident factions who have persisted in it.

Perhaps most important, the largest and oldest guerrilla group, the pro-Moscow Colombian Revolutionary Armed Forces, has announced that it is converting into a political party and hopes to compete in next year's elections. Many of its estimated 10,000 members are said by government officials to have returned to farms and towns in the countryside.

"The peace process is now irreversible," said Agudelo. "It is too late for anyone to turn it back."

The fulfillment of such predictions would be a vindication of the personal leadership of Betancur, who since taking office in August 1982 has made peace initiatives both at home and in the Contadora group in Central America the focus of his administration.

To a large degree, Colombia's pacification has been shaped by Betancur's personal dealings with guerrilla leaders and by the extrainstitutional organizations that have sprung from them, including three special government commissions.

The result has been a fluid, flexible process that has allowed the president to improvise freely and win a certain loyalty from guerrilla groups. "As long as Betancur is president, the guerrillas won't play dirty," predicted Santos Calderon. "They have a personal complicity and commitment with him at this point."

If Betancur's personal style has helped carry the peace initiative through its worst crises, however, it has also helped spawn several serious long-term problems, critics say. "The political parties and the Congress have been witnesses to all this, not participants," said Ernesto Samper, a leader of the Liberal Party, the traditional rival of Betancur's Conservatives.

"The process has been improvised. So it has no real political backing."

For Colombia's traditional political establishment, the chief example of the government's errors is the National Dialogue, a series of commissions established to study possible social and political reforms under the agreements signed by Betancur with the M19 and two other guerrilla groups last summer.

Made up of guerrilla leaders and politicians and businessmen appointed by the government, the commissions are meant to agree on concrete measures that the government would then consider for submission to Congress. Liberal Party opposition leaders say the bodies usurp the role of Congress and local governments and are not capable of producing proposals.

"The dialogue is a waste of time," said Samper, who added that he has not bothered to attend the meetings of the commission to which he was appointed. "It is only a collection of people making speeches to each other, a kind of United Nations for guerrillas."

Government officials defend the dialogue as a mechanism for including guerrilla groups in the official establishment. However, the lack of political consensus, combined with the approaching election campaign, has endangered the series of changes already proposed to Congress that guerrilla leaders view as essential to their inclusion in the democratic system, political leaders say.

The changes would include opening radio and television time to electoral candidates outside the two main parties, public financing of campaigns and direct election of mayors and state governors now appointed by the ruling party.

"What is going to happen if we don't approve the political and social reforms and include these groups in the next election?" asked Samper. "There is going to be a tremendous frustration and temptation to return to violence."

Already guerrilla organizations like the nationalist M19 are complementing rhetorical support for the goal of abandoning armed struggle with attempts to maintain camps in the countryside, concentrating heavily armed military forces.

Government officials now say that guerrilla groups will not be allowed to participate in the national elections unless they first give up their arms. The insurgents' spokesmen, meanwhile, are saying that no such integration into the system will be possible without the approval of the political changes.

These conflicting stands, say both sides, are likely to provoke another showdown between guerrillas and the government and a major test for the peace process in Congress.