Former premier Aldo Moro, one of Italy's key political figures, was kidnapped yesterday in an armed attacked that killed his five body-guards.

The Red Brigades, Italy's lefist urban guerilla group, claimed responsibility for the abduction. Moro, who is president of the ruling Christian Democratic Party, is leading contender for the presidency of Italy.

Moro's sedan, accompanied by a police car, was ambushed on a Rome street as the politician, 61, was on his way to a parliamentary meeting at which Christian Democratic Premier Gulio Andreotti was to ask for a confidence vote on Italy's first Communist-supported government in 31 years.

Telephone calls by persons purporting to be members of the Red Brigades described the kidnapping as "an attack on the the heart of the state." It appeared designed to destabilize Italy's internal situation and possibly force suspension of a scheduled trial of several suspected Red Brigades terrorists.

Moro's fate was not known. Traces of blood in one of the cars used by the terrorists and later abandoned have led to police speculation that he may have been wounded in the hail of bullets that sprayed his car.

After the kidnapping, the parliament altered its procedures and gave a massive vote of confidence last night to a new Andreotti government.

The government mounted a manhunt of unprecedented scope that turned Rome into a besieged city.

Moro, a five-time premier and former minister of foreign affairs, justice and education, had just said mass in a neighborhood church and was headed downtown, along his usual route to Christian Democratic headquarters.

The attackers, four of whom were reportedly dressed in the uniforms of Italy's national airline, Alitalia, apparently arrived on the scene in as many as three cars and possibly a motorcycle.

In a scenario reminiscent of the kidnaping last year of West German industrialist Hans Martin Schleyer, later murdered, one of the cars driven by the terrorists blocked the path of Moro's sedan while other terrorists used machine guns to kill his armed escorts.

Police said that some of the bullets from the terrorist's guns appeared to have come from a rarely used Soviet-made weapon and a Czechoslavak-made Nagant pistol. The latter weapon has been used by the Red Brigades in at least seven other recent shootings.

By last night Police said no specific Red Brigade demands had been recieved. There was widespread speculation, however, that the terrorists would ask to exchange Moro for the 15 imprisoned Red Brigades members being tried at Turin.

About 50,000 army troops and police, aided by helicopters and tracker dogs, have been thrown into the search for Moro and his captors. According to witness, 11 men and a women were involved in the kidnapping.

Meanwhile, Italy's major unions have called a one-day work stoppage to protest the terrorist attack.

All Italian political parties condemed yesterday's attack. President Carter called it "an outrage" that "deeply affects us all. "Pope Paul, in a message to Moro's wife said he was praying that "the authors of this tragic attempt return your dear husband unharmed." The Soviet news agency Tass described the attack as a "dangerous provovation" by "the forces reaction."

Earlier yesterday Premier Andreotti, a close assosciate of Moro's for more than 30 years, addressed a tension-ridden parliament with a plea for "firm-nerves."

Andreotti said the kidnaping must not be allowed to interfere with a painstakingly negotiated program recently worked out by five parties, including the Communists.

Andreotti's sentiments were echoed later in the day by Communist Party leader Enrico Berlinguer who called for an immediate vote of confidence for the new Christian Democratic government, to which the Communists have agreed to give official parliamentary support.

Berlinguer described Moro as "one of the most eminent figures in Italian political life" who was instrumental in persuading his fellow Christian Democrats to allow the Communists to win a formal role as part of the voting majority. In the early 1960s he played a similiar role in inaugurating the series of center-left governments that were based on a Christian Democratic-Socialist alliance.

Conservative and progressive politicians here disagreed over whether the Red Brigades' tactics were designed to push the Communists closer to power or to disrupt a budding Christian Democratic-Communist alliance by encouraging a rightist backlash.

But the general feeling here was that yesterday's kidnapping and murders were likely to strengthen the current trend toward Catholic-Marxist cooperation rather than interfere with it.

Last year Italian police tallied a total of 2,128 terrorist acts here, although many were cars burnings and other minor arson cases. The Red Brigades are the best organized and most feared of at least 30 lefist "revolutionary" groups currently operating here.

In recent years the Red Brigades have escalated their violence from breaking and political to scores of leg shootings and at least eight murders.

Last week in Turin a four-man Red Brigade commando murdered a non-commissioned police officer in an attempt to intimidate judges, lawyers and jurors at a trail there of several alleged Red Brigade members, including the group's founder, Renato Curcio, 36.

Moro was the highest ranking politician to be attacked by the Red Brigades. Most attacks have been against politicians, businessmen and journalists.

Born in Lecce, in the southern Italian region of Apulia in 1916, Moro was first elected to parliament in 1946.

A slow-speaking fragile looking man who is known for his passion for afternoon moviegoing, Moro has never been won points for his capacity as an administrator. He is, however, considered the principal theoretician of the Christian Democratic Party, and observers here generally agree that over the past 15 years his mediatory capacities have been primarily responsible for keeping the Christian Democrats firmly in the saddle of Italian political power.