In 1977, communiques were issued by 120 different underground Italian leftist groups.

Specialists say that more than half of the exotically named organizations were in fact nothing but tiny ad hoc groups of people trying to get their messages across by creating an impression of tremendous revolutionary ferment.

But the experts say there undountedly are about 30 real group with about 1,000 members actively waging guerrilla war - with varying degrees of ardor and effectiveness - against the Italian state. Bolstering them are thought to be several thousand active supporters.

The Red Brigades are apparently the largest and best organized part of the extremist underground that is itself only a fraction of a disaffected mass that found little general support until the Communist Party dropped its revolutionary rhetoric.

In the last parliamentary elections, in 1976, the far left won about 700,000 votes, or 1.5 percent of the total.

Its breeding ground is among the 1.2 million unemployed young people between 18 and 29 and among the nearly 1 million university students, especially universities of Rome, Milan, Turin, Genoa and Naples.

A large portion of the unemployed are migrants from southern Italy, a region that remains economically depressed despite major government efforts to stimulate its development. Move to Cities

In 20 years, 10 million people have left rural areas to crowd into the cities, which have tripled in population. Turin, the Fiat auto factory city, has doubled in population in a decade.

It is widely believed that the red brigades are primarily the children of the middle class with university educations. There is some of that. Alessandor Silj, a journalist whohas studied the Red Brigades, tells of seeing students at violent demonstrations looking at their watches and rushing home for lunch because they were afraid their mothers would be angry if they did not show up. Even a couple of children of kidnaped former Premier Aldo Moro are extreme leftist.

Yet, Silj found in his study of the Red Brigades leaders, "Never Again Without Guns," that while most have attended university, about half are from worker familes and many from the south. When people move north, he concluded, family units often break up and the traditional constraints of family, the Catholic church and even of the Mafia disappear.

The extreme leftists are also part of a milieu that is in open rebellion. The Red Brigades get sympathy if not support in those groups. "Neither with the state nor with the Red Brigades" is a slogan that has gained wide currency among them.

The Communist Party, which has been losing its grip on youth, attacks the slogan as amounting in practical terms to support for the Red Brigades.

The youth wing of the Communist Party declined by 10 percent last year, according to the party's own figures. Maoist groups, once popular with extreme leftist youth, have virtually disappeared as a political force since the Chinese Communist leadership has charted a more moderate course.

Giuseppe Boffa, an editorial writer for the Communist Party newspaper L'Unita spoke in an interview of the indulgence the nonviolent extreme leftists have for the Red Brigades. "They cover the terrorists," he said. "They even serve as couriers for them sometimes. In any case, there is a certain Omerta surrounding terrorism." Omerta is the law of silence that protects the Mafia. Eye of the Hurricane

Franco Ferraroti, the head of the sociology faculty of the University of Rome, is in the eye of the hurricane. The 10,000 Roman sociology students provide the hard core of the hard core. He has told of being mugged and beaten by his own students.

Ferraroti blames the government for creating a large part of the conditions for discontent by giving in after the 1968 student revolt to demands to open the universities to anyone who wanted to enroll. As a result, he saids, Rome University has 170.000 students in facilities built for 25.000.

There are no dormitories and the students lodge themselves as best they cab around the city. Except for the Roman students, who live at home and are a minority, the student life is a rootless existence in which political activity is the easiest social outlet.

Neo-fascists and extreme rightists have practically disappeared from the universities, according to Ferraroti. The student and intellectual milieus of Rome are almost exclusively leftist. So, Ferraroti said, the Red Brigades are not isolated like the Baader-Meinhof terrorist group in West Germany. "Old Family Album"In a visit to the offices of Luto Continua, the leading organ of the legal extreme left, on a grubby back street of Rome, most of the staffers were clean-scrubbed, short-haired people on their early 20s. They looked like they could have been taken off a 1950s American campus.

Paolo Brogi, in his mid-30's, appeared to be the oldest person on duty. He repeated a statement now common within the Italian extreme left: "Reading the communiques of the Red Brigades is like leafing through an old family album." He said that much of their Leninist rhetoric sounds outdated, but that it is recognizable as part of the history of the left.

The Red Brigades come out of the same experience as his own group, Brogi said the 1968 student-worker revolt that spread across Western Europe after the May-June riots in Paris. The movement was more spectacular in France, Brogi said, but in Italy it lasted longer, grow deeper roots and the students succeeded in creating permanent links with the workers.

"We don't condemn violence," he said, "because the order under which we live is very violent. But we don't condone murder. Unlike the 111Red Brigades, we see our stuggie as being against institution. We don't consider our adversaries symbols to be personally destroyed."

Nevertheless, he said there are those in his amorphous movement who approved of the Moro kidnaping. "There is a daily temptation," said Brogi, "to deny the Red Brigades. We are being blackmailed into condemning anti-parliamentarianism. But we know who the Red Brigades are. They are not mysterious objects. They were with us in 1986."

According to Boffa Vnita, "For the people in Lota Continus, the Red Brigades are simply comrades who are mistaken but have good intentions."

"There is a myth, a romance to clandestinity," Brogi said, adding that it has been reinforced by the "historic compromise" between the Communists and Christian Democrats.

To the people in the underground, he said, "Italian politics seems to be a closed universe that brings together the near-totality of political forces.'

The underground, he said, is "the meeting place of despair."