After they called him a hero and before they called him a traitor, El Salvador's guerrillas used to call Arquimides Antonio Canada "the lost commander."

The stocky, self-assured 28-year-old who used the nom de guerre "Alejandro Montenegro" was a member of the powerful People's Revolutionary Army faction of the five-member guerrilla front. As a top officer on the Guazapa Volcano, a guerrilla stronghold that overlooks the capital, he plotted the spectacular sapper raid that destroyed most of the Salvadoran Air Force in January of last year.

"We have the political and military initiative all over the country," he proclaimed afterward.

But on Aug. 22 Canada was in a little restaurant in the capital of neighboring Honduras when members of the Honduran Army's special U.S.-trained Cobra unit caught up with him. He disappeared into what American military men in the region described discreetly as "the intelligence community."

When Canada reemerged six months later on prerecorded interviews with vague and mysterious origins that were shown in the region he was affirming virtually every point the U.S. and Salvadoran governments are trying to make about the war here. He told of receiving training and orders from Cuba. He said last year's elections were a resounding political defeat for the rebels and he concluded that "the guerrilla movement has lost its support."

For the last two nights Canada has said much the same thing over the U.S. government's Voice of America. According to VOA officials, the recording session took place in their Washington studios Saturday, but they did not explain exactly how or who arranged it and they said they believed that Canada had once again left the country.

Between Canada's arrest in Tegucigalpa and that relaxed chat with the Voice of America lies a tangle of secret interrogations, accusations of brainwashing and duplicity and an odd series of travels that wound up shaking not only the oft-feuding guerrilla factions but also the officers who run the U.S.-backed Salvadoran Army.

For much of the time that Canada was out of sight his fate appears to have been bound up with that of then deputy defense minister Francisco Adolfo Castillo, a prisoner of the guerrillas. The well-liked and respected colonel had been trying to visit front-line troops when his helicopter was shot down last June 17. He was, both the guerrillas and apparently his family believed, the logical subject for a trade.

Immediately after Canada was picked up in Tegucigalpa, along with six other Salvadorans, the rebels tried to raise the stakes.

On Sept. 17, a small group of Salvadoran-allied guerrillas from a Honduran group calling itself the "Cinchoneros" burst into the San Pedro Sula Chamber of Commerce and took about 100 hostages, including two Cabinet ministers, demanding the release of Canada and scores of other alleged Honduran political prisoners.

But in the first move of what eventually became a sort of human shell game, the Honduran government announced that Canada and the other six already had been deported to El Salvador as illegal aliens. The hostage siege ended peacefully after a week.

According to one usually well-informed U.S. official in the area, the Hondurans "apparently were treating Canada in typical Central American fashion," which the official said he might not have survived. According to this official, when the United States confirmed who had been picked up it had him taken to El Salvador for a protracted period of interrogation.

"They treated him well," the official said, but added, "They really did a job on him."

Salvadoran government officials publicly acknowledged getting Canada and the other six from Honduras at the time.

Soon afterward, according to rebel accounts of the proceedings on their radio station and in their publication, talks were begun about exchanging Canada and the other six along with another imprisoned commander for Col. Castillo.

"We don't know anything about any exchange," said a Salvadoran armed forces spokesman yesterday, ruling out any negotiations or dialogue concerning Castillo at any official level in the past, present or future.

But the rebels have published several letters purportedly sent to Castillo by his wife in which she talked about promises made to her by various members of the high command and especially then chief of staff Col. Rafael Flores Lima about a possible prisoner exchange toward the end of the year.

Mrs. Castillo "has the full right to explore all ways to free her husband," said the military spokesman. "She can do what she wants but that is not in any way a negotiation by the government or armed forces."

On Nov. 18, according to Panamanian intelligence officials, Canada and the other six arrived at Panama City's International Airport in the company of two Americans. They were subsequently taken to the Howard/Kobbe U.S. military complex for several days, these officials said.

On Nov. 27, a photograph of the seven at the airport appeared in the Panama City daily Critica.

"The lives of seven exiles are saved and Panama plays the role of mediator," read the accompanying caption, adding that the Salvadorans had passed through the country some time before but did not want to make any statements.

One top official of the guerrilla movement said recently that the photograph was interpreted by the guerrillas as an attempt to convince them that Canada and the rest had already been released so that the rebels would proceed with plans to release Castillo. But the rebels were not persuaded and by the end of the year the chances of an exchange were rapidly declining.

In February, El Salvador's president named Flores Lima to replace Castillo as deputy defense minister.

On March 3, Arquimides Antonio Canada appeared in a videotape broadcast over Salvadoran television without any previous announcement. At the same time, Salvadoran government forces attacked several guerrilla positions on Guazapa and inflicted what the rebels conceded were extensive damages and casualties.

Nine days later, the rebels' Radio Venceremos denounced Canada as a traitor, noting that numerous other guerrilla leaders had suffered lengthy interrogations, torture and death without compromising their fellow rebels and without issuing statements damaging to the rebel cause.

The guerrillas also broadcast an extended statement by Castillo in which he lauded the strength, effectiveness and sophistication of the rebel army, while blasting his former schoolmates and fellow officers as corrupt, brutal and ineffective.

In language reminiscent of the guerrillas', Castillo talked about "the tracks of genocide made by the Atlacatl Battalion commanded by Lt. Col. Domingo Monterrosa." The former deputy defense minister denounced Col. Onecifero Blandon, commander of the 1st Brigade and a rising star in the armed forces, as one of those "who have reached the point of making themselves into smugglers of arms and drugs."

After such statements, it may be that both men will soon appear free. As one senior U.S. officer in the area said, referring to rumors that Castillo may already have been set free in Nicaragua or another country, "We don't know for sure, but we think it's true. He can't go back to El Salvador in any case after the things he's said."

As for Canada, a Voice of America spokeswoman said he may be living in Costa Rica.