Former Italian premier Aldo Moro, whose kidnaping by Marxist urban guerrillas 55 days ago stunned his country and the world, was found shot to death here yesterday.

The body of the 61-year-old politician was discovered in the back of a parked car in downtown Rome where his Red Brigades kidnapers left it after pumping at least nine bullets into his chest and head. There were indications that Moro was shot early yesterday morning, possibly when he was already inside the car.

The discovery, which came after police intercepted a phone call from the radical terrorists to Moro's office, brought millions of Italians into the streets, climaxing a national ordeal to which Italy has been subjected since his capture.

The car was parked on a small street around the corner from the headquarters of both the Christian Democratic and Communist parties. Moro, his hands and feet chained, lay curled up in the back of the car, his chin sunk onto his chest. He was clad in the same dark gray suit he was wearing when kidnaped in a March 16 street ambush in which five of his bodyguards were killed.

At least four shells were reported found in the car, suggesting the killing may have taken place inside the vehicle. Those who saw the body being removed by police said Moro's expression was "scene" and that his face had several days' growth of beard. A small plastic bag near the body contained Moro's watch and a thin gold bracelet.

While scores of police held back reporters and the crowds of onlookers, a priest from the nearby Church of Jesus performed the rites of extreme unction before Moro's body was taken to a morgue.

Moro's embittered family, which had pleaded vainly with the ruling Christian Democrats to bargain with the terrorists for his life, immediately issued a statement ruling out a state funeral or other official mourning ceremonies, as Moro himself had requested.

The Christian Democratic Party of which Moro was president, refused to deal with the terrorists, rebuffing Moro's pleas in several letters written during the captivity.

Premier Giulio Andreotti, following an emergency session of his Cabinet, decided to respect the family's wishes and made no special declaration. Italy's giant trade union federation, however, called a general strike yesterday and scheduled a second, shorter work stoppage for today, while President Giovanni Leone scheduled an address to the nation.

Christain Democratic Party secretary Benijno Zaccagnini, a long-time friend of Moro's, chocked back tears as he tried to express his sorrow. Communist Party leader Enrico Berlinguer described Moro as "a great democratic leader slaughtered by an organization of criminal terrorists."

The Red Brigades, flaunting to the end what they called their attack on the "heart of the state," left Moro's body who blocks from Rome's busiest intersection, around the corner from Communist Party headquarters and only a stone's throw from Christian Democratic headquarters.

The location was symbolic since Moro was the chief architect of a recent agreement between the two parties which gave Italy its first government with formal Communist support in 31 years. At the time of Moro's kidnaping, it was widely believed here that the Marxist terrorists were aiming to disrupt the burgeoning alliance between the country's two largest parties.

Last night, crowds jammed Piazza del Gesu outside of Christian Democratic headquarters for an all-night vigil and a late mass at the Church of Jesus next door.

At Rome's ancient Coloseum, the red flags of the Communist and Socialist parties and the white flag of Christian Democrats were held aloft as tens of thousands of Romans attended a rally to hear from Rome's Communist mayor, Giulio Carlo Argan. Demonstrations were held throughout Italy and the country's flags flew at half staff.

Yesterday's killing of the five-time premier sent shockwaves throughout the country, although last Friday's communique from the Red Brigades had virtually foreclosed all hope for Moro's survival. In that communique the terrorists announced that "we are ending the battle begun on March 16 by carrying out the sentence to which Aldo Moro had been condemned."

Following his kidnaping, the Red Brigades had announced that a "people's court" had sentenced Moro to death. The sentence was passed for what they termed to be Moro's participation in "an offensive against the proletarian movement" and in "the political genocide of the Communist vanguard" carried out by Italy's ruling Christian Democratic party over the last 30 years.

Subsequently, the Red Brigades said Moro's death sentence could be "suspended" and Moro released only if the government would agree to free 13 jailed terrorists.

Andreotti's cabinet, backed by both the Christian Democrats and the powerful Communists, took a hard-line position and - despite a series of anguished letters from Moro - ruled out any negotiations.

The terrorists ignored appeals for Moro's life from both Pope Paul and U.N. Secretary General Kurt Waldheim and ridiculed "humanitarian" proposals regarding prison reform made by the small Socialist Party.

Throughout the period of Moro's captivity, the Red Brigades, which began operating here in 1970, kept up the pace of their other terrorist attacks. Since March 16 they have murdered two prison guards, in Milan and Turin, and, along with a smaller terrorist organization, shot and wounded another 10 people. The Red Brigades have killed 10 people so far this year.

Moro, however, is the most influential and highest ranking politician ever to be attacked and killed by terrorists in Western Europe. Because of his skills as a mediator, he held a special place in Italy's high fractured political system.

With an important round of local elections scheduled for Sunday, Moro's death is likely to have an immediate impact, with both the Christian Democrats and the Communists seeking to defend the hard-line, no-negotiation position that likely will be attacked by some groups as the indirect cause of his death.

Should the Socialists and some groups within the Christian Democratic Party take such a position, it could have a negative effect on the stability of Andreotti's minority government whose survival depends on the parliamentary support of five parties, including the Socialists.

But Moro's disappearance from the political scene could have longer-term implications as well, especially because of his political skills.

Many observers here are convinced that Italy's serious social, economic and public order questions make a role for the Communist essential for the time being if Italy is to be governed.