Like a scene from "Blackboard Jungle," students at Milan's Cesare Correnti vocational high school recently threatened to throw dentistry professor Claudio Francesconi out of a window.

Yet the attempts at teacher intimidation and the acts of voilence currently troubling Italian high schools have little to do with juvenile deliquency as Americans know it.

Graffiti scrawled on the walls of high schools in Rome are primarily political slogans that praise Lenin and Stalin, denouce Italy's "bourgeois, capitalist society" and explain why a group of highly politicized youngsters are demanding that every student be given a "political 6" - an automatic passing grade.

The debate over the "guaranteed 6" flared her early this month when the Ministry of Education sent inspector Salvatore Candido to Milan to investigate the turbulence that has plagued on of that city's largest vocational schools for months.

Reports had described teachers attacked or threatened, much of the school's premises and property covered with splashes of paint, and the principal, Maria Giovanna Origlio, openly referred to as "the whore."

But the worst blow for Candido came later with his discovery that for years many of the teachers had bowed to pressures from a minority of the school's 2,000 students to give everyone a grade of at least 6 (out of a possible 10) or else.

"Whoever fails a student, dies" and "A failed student means a massacred teacher" were slogans painted at the school's entrance and flanked by the five-pointed star used by the Red Brigades," Italy's best-organized and most notorious, political terrorists.

The debate set off by the inspector's Milan visit brought cries of conmcern from most of Italy's educators and from all of the traditional political parties, including the Communists, whose student organization has lost considerable ground to leftist extremists called "autonomi" because of their refusal to belong to a specific group.

The primary effect was to reveal that the Milan example is not alone. Earlier this year at a Rome vocational high school, the Marconi Institute, a young Communist teacher named Margherita Pinna was temporarily kidnaped and given a mock trail by extremists, who accused her of "repressive" behavior because she had telephoned the parents of a student who had played hooky.

At the Sarpi science high school in Rome, a long list of violent actions includes the beating of the principal, the burning of his car, destruction of completed math exams and arson in the staff room.

In all of these schools, attended primarily by students from working-class families, a violence-prone and intolerant minority has been calling for guaranteed promotion to end what Marxists call "class selection" and the "repressive" school system.

"No one can take away our right to a passing grade," said a 15-year-old student at Sarpi high. "It is the point of departure for new struggles against factory exploitation," another told a student assembly. A 17-year-old at Cesare Correnti insisted that "a passing grade for everyone is a major goal because it gives us a slice of power and takes a repressive instrument away from our teachers."

Weary of waiting for a long-overdue school reform, many of the high school protesters are convinced that the present system discriminates against the poor since "private school students have the money to make sure that they will all get a guaranteed 6."

Observers here have compared these extremists to the Luddites of the early 19th century who thought they could stop the burgeoning Industrial Revolution by smashing machinery.

The majority of students, however, including Communists and other far-left student militants, still believe that guaranteed promotion makes study worthless and does not redress the inequities of Italian society.

The extremists' attitude is a sign of the extreme frustration of youngsters caught between the promises of consumer society and the bitter realities of the current economic recession. It also appears to represent a wide spread sense of disillusionment with the current value of a high school degree.

At a recent Rome student-teacher meeting, a teen-age girl put it this way: "We don't give a damn about studying nor about discussing matters with you. Education is a waste of time. Being together is the only thing that counts for us."