The Red Bridges terrorists who have held former Italian Premier Aldo Moro prisoner for the past month announced last night that his "people's trial" was over, and that the influential Christian Democratic leader had been condemned to death.

The communique, the sixth since the Red Guards kidnapped Moro and killed his five bodyguards in a bloody ambush March 16, set no date for his execution.

Immediately after the first copy of the message was received in Genoa, high-level government officials rushed to meetings at the Interior Ministry, while key politicians sped to the headquarters of Christian Democratic and Communist parties to discuss the communique's contents.

A spokesman for Premier Giulio Andreotti's minority Christian Democratic government said there was "great concern" for Moro's safety, but "considerable hope" that the death sentence was primarily a move by the Red Brigades to "further dramatize the situation."

A spokesman for the Communist Party, which officially supports the Andreotti government in Parliament, said it was entirely possible that the Red Brigades messages have come on Saturdays because on a Sunday, "they get maximum coverage and only a minimum of reaction."

In their communique, the Red Brigades said Moro's trial was "only one stage" in its overall war against the state and against the government.

As in their previous five messages released since Moro was kidnaped and subjected to trial as the country's principal "political godfather," the Red Brigades made no demands and failed to lay out any conditions for the release of the high-level Christian Democrat.

From the start the Italian government and all of Italy's major parties have ruled out the possibility of any deals with the terrorists. Nevertheless, the new message sent shock waves through Rome where, judging from the weekend absence of many top politicians, a move of this sort had not been expected, at least for the moment.

The Red Brigades' last message a week ago included a long statement by Moro in which he attacked a high ranking Christian Democrat and former cabinet minister, Paolo Emilio Taviani. Similar attacks against other party representatives had thus been awaited before any further major developments.

But the Red Brigades, in a communique received by news organizations in four Italian cities, said the former premier had been convicted for his part in the "offensive against the proletarian movement" allegedly carried out by the Christian Democratic Party during its past 30 years in power.

"The responsibilities of Aldo Moro are the same as those for which this state is on trial," the communique said. "There is no doubt that Aldo Moro is guilty and he has therefore been sentenced to death."

The message spelled out the sins of the Christian Democratic party, which it described as the "watchdog of the bourgeoisie," and said that during his trial Moro had disclosed "facts and names" regarding the major scandals of the last 30 years.

But it also said that there would be no "sensational revelations," leading to speculation here that in 31 days of captivity Moro may not have "talked." "If they kill him it is a sign that either he has already told them everything he knows, which appears doubtful, or that he is not proving to be useful," the Communist spokesman said.

The Communists, whose current as a member of the parliamentary majority was worked out by Moro shortly before he was kidnaped, have said from the start it would not use any disclosures made by Moro against their Christian Democratic partners and rivals.

The Communist believe that the Red Brigades deliberately planned their kidnaping of Moro for March 16, the day that Andreotti went before the parliament to present the country's first Communist-supported government in 30 years.

The Christian Democrats feel that the major purpose of the abduction was to discredit their party's major strategist and theoretician and at the same time to try and undermine its unity and sense of purpose.

Both groups, however, agree that the attack on Moro as well as his possible death is part of the Red Brigades' much publicized plans to launch an attack "on the heart of the state." The leftist extremists, who began operating here in 1970, are known to believe that unchecked terrorism will lead to a police crackdown and ultimately to a popular uprising.

For this reason, said a government spokesman, "our primary attitude will be and is one of calm. The aim of the Red Brigades is to shake the foundations of the state. If we remain calm, for them it is a defeat."