Terrorists who seized former Italian Premier Aldo Moro five weeks ago released a photograph yesterday that indicates that the influential Christian Democrat is still alive.

Messages circulated by the Red Brigades terrorist group yesterday gave the Italian government until Saturday to release Communist prisoners in Italian jails in exchange for Moro's life.

After the release of the snapshot, showing Moro with a Wednesday edition of a Rome newspaper, Italian authorities called off their frantic three-day search for his body in the frozen waters of a lake in the mountains northeast of Rome.

The messages attributed to the Red Brigades yesterday said that an earlier communique attributed to the terrorist group claiming that Moro had been killed and thrown into the lake was a hoax and a "provocation."

While yesterday's development came as a relief to an Italian government that had been prepared to find the body of one of its leading political figures, it also created a major dilemma for the minority Christian Democratic government.

Since Moro's kidnapping, the government - which is supported in parliament by the powerful Communist Party as well as several smaller parties - has insisted that no negotiations are possible with terrorists "whose hands are dripping with blood."

But the government of Premier Guilio Andreotti was certain to come under pressure from Moro's family and friends, as well as a number of Christian Democratic and Socialist politicians who believe negotiations should be opened.

The snapshot of Moro, which was left in a waste basket for a reporter from the Rome daily, II Messaggero, shows Moro holding a Wednesday edition of the Rome paper La Republica. Moro, dressed in a white shirt, appeared to be in good health.

Police, firemen and frogmen had been searching for his body in the isolated area of Lake Duchessa for three days. Yesterday there was a moment of panic when police bloodhounds discovered a body in nearby Lake Salto. But the corpse was that of a 45-year-old shepherd who neighbors described as mentally retarded.

So far there has been no satisfactory explanation of the Tuesday message claiming Moro had been killed. But some intelligence sources speculated it was done deliberately to raise the level of tension and to prime Italy's political establishment for yesterday's ultimatum.

The new message, which intelligence and Interior Ministry sources have described as almost certainly authentic, reiterated Moro's death sentence, first mentioned in a message issued last Saturday, and rejected recent humanitarian appeals by the Christian Democrats.

"The release of the prisoner Aldo Moro can be taken in consideration only in relation to the liberation of Communist prisoners," the message said.

The Red Brigades, who kidnapped Moro on March 16 after murdering his five bodyguards, did not give any names but were thought to be refering to the more than 300 leftwing extremists in Italian prisons. Fifteen of these, alleged members of the Red Brigades organization, including founder, Renato Curcio, are now on trial in Turin.

It suggested that the Christian Democrats "give a clear and definite answer" adding that - "It must be clear that no other possibilities exist."

It set a 48-hour ultimatum expiring at 9 a.m. EST Saturday. Otherwise the message continued, "we will take upon ourselves the responsibility for carrying out the death sentence issued by the Prople's court."

The determination of the terrorists was underscored by a new murder yesterday morning in Milan that was claimed by the Red Brigades.

A three-man gang pumped seven shots into Francesco De Cataldo, 53, a prison guard who the terrorists claim was "a torturer of prisoners." It was the second murder of a prison guard in less than two weeks and the ninth murder by the Red Brigades so far this year.

Top officials of the Christian Democrat Party met late yesterday after attending a Mass for Moro.

An editorial published in today's edition of the official party paper, II Popolo, expressed joy at learning Moro is still alive, but condemns the Red Brigades' latest murder and says that the Christian Democratic Party is a private organization that cannot be identified with the state and "cannot give what it has no right to give."

Communist Party leaders met and reiterated their hardline position against negotiating with the terrorists and giving in to their "blackmail." A similar position was taken by three smaller parties, the Liberals, Republicans and Social Democrats, while the Socialists, who often make a point of differentiating themselves from the Communists, seemed to vacillate.

The Communists appear convinced that any concessions to the Red Brigades would be tantamount to giving them recognition and legitimizing the use of violence. They are fearful that vacillation by the Socialists or the Christian Democrats could lead to a new government crisis and would represent a victory for the Red Brigades.

Until yesterday the Red Brigades had made no specific demands for a prisoner exchange, although Moro had mentioned it in several of the letters he has written from captivity.

The only recent Italian precedent for such an exchange occured in 1974 when the Red Brigades kidnaped Mario Sossi, a Genoa judge, and held him for six weeks. They commuted his "death sentence" when another judge ordered the release of several jailed terrorists.

After Sossi's release, the attorney general of Genoa, Francesco Coco, revoked the order. Two years later he and his bodyguards were murdered by the Red Brigades.