Otelo Saraiva de Carvalho, the military mastermind of the almost bloodless revolution that returned Portugal to democracy in 1974, went on trial today, accused of leading a leftist urban guerrilla group responsible for a wave of assassinations and bombings.

The trial was adjourned within hours because of the absence of a defendant who had become a key prosecution witness and who was shot and seriously wounded Friday night in an attack claimed by the guerrilla group that Saraiva de Carvalho allegedly led.

More than 50 defendants raised their fists in a revolutionary salute at the start of the hearing in a specially built, fortified courthouse on the grounds of a Lisbon jail. Smiling and relaxed, former Army colonel Saraiva de Carvalho, 48, pressed against the bulletproof glass a note saying, "The trial is a farce . . . we the accused will for certain become the accusers."

The ex-officer is charged with founding, leading and promoting a terrorist organization alleged to have murdered at least six industrialists and police in bomb attacks, shootings and bank holdups during the past five years.

Actions claimed by the group include mortar attacks on NATO warships anchored in Lisbon harbor and the U.S. Embassy, along with a $600,000 robbery of an armored car.

Presiding Judge Adelino Salvado adjourned the hearing until Oct. 7 after noting the "terrifying circumstances" that led to the absence of the wounded Jose Rosa Barradas. He was one of five so-called repentant defendants on whose testimony much of the prosecution case reportedly rests. A state prosecutor said the others were at serious risk and arranged for them to be separated from their fellow accused.

The shooting of a principal witness who was under police protection has raised criticisms of security despite the rigorous measures taken around the $570,000 courthouse, built for the trial in three months.

Inside, demonstrators shouted "Otelo, Otelo," and Saraiva de Carvalho was admonished by the judge as the ex-colonel stood embracing and greeting his fellow defendants. They had been held separately since their arrest 13 months ago.

A bluff officer with close-cropped silver hair, he was one of the best-known figures of the "Revolution of the Carnations" that brought people into the streets with flowers for the soldiers and overthrew 48 years of right-wing dictatorship.

Saraiva de Carvalho was arrested following a police sweep in June last year when allegedly incriminating documents were found at the headquarters of the small leftist party he has led since failing in his second bid for the presidency in a 1980 election. The prosecution charges the party was a front for a clandestine organization intent on "the violent transformation of society."

Saraiva de Carvalho and all but five of the accused deny the charges, which carry jail sentences of 10 to 20 years, and any connecton with the April 25 Popular Forces, that takes its name from the date of the 1974 coup.

About 40 other suspects were detained in the operation launched a day before a parliamentary debate on a controversial government anti-terrorist bill that opponents fear could lead to a return of the methods of the former regime's notorious political police.

The timing of the crackdown and the debate highlighted the political overtones of the guerrilla case. But Rui Machete, then justice minister, rejected claims that the police sweep was carried out to demonstrate the need for strengthened security.

The threat of voting rebellion within its own ranks forced the government to pledge a drastic toning down of the bill. It had not become law when the ruling coalition of Prime Minister Mario Soares collapsed in a row over economic policy last month.

The case has raised claims that Saraiva de Carvalho is on trial more for his leftist political views than his alleged crimes.