With the Panama Canal treaties signed, the government today began to prepare the Panamanian capital for its own domestic consummation of the event.

The "public catharsis," as one reporter called it, will be a grandiose "welcome home" rally for ruler Brig. Gen. Omar Torrijos and his large delegation as they arrive from Washington Friday afternoon. The rally will be held on the Fifth of May Square, just a few hundreds yards from the Canal Zone.

The authorities have drafted the nation's buses, taxis and trucks to ferry in thousands of people from Panama's coast and highland.

The nearly 100,000 government employees have been told to attend, as have labor unions and rural organizations.

As the climax of the rally, Torrijos is expected to hand copies of the signed treaties to the head of state, President Demetrio Lakes. The date of the ratification plebiscite reportedly will then be announced.

The government has promised an open public debate of the issues, but anti-treaty demonstrations apparently will not be tolerated. Yesterday and today students of the leftist Revolutionary Student Front skirmished with Panama's National Guard, which has strict orders to keep dissidents off the streets. According to press reports 31 student demonstrators were arrested yesterday and some youths who threw a fire bomb were picked up today as well.

The militant student groups from the university and high schools are causing serious concern among authorities in the Canal Zone.

While the Torrijos government has organized other nationalist rallies on the Zone doorstep, there is genuine fear this time that uncontrolled groups will want to stage a symbolic takeover by marching into the U. S.-controlled enclave.

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Such a symbolic flag-raising ceremony violent clashes that killed 21 Panamanians and three Americans in 1964.

The mothers of the 21 Panamanians have been invited to Friday's ceremony, where they are to receive special tribute.

Despite his past inflammatory anti-American rhetoric, however, Torrijos is known to oppose any incursions into the Zone that might lead violence.

Torrijos recently surprised American officials here by saying in a speech that "If the U. S. Senate does not ratify the treaty, we must find an answer that is not violent." Rejection of the treaty "will be a provocation to which Panama must not respond," he said, because a violent response would only "provide arguments for Carter's enemies." In a recent press conference Torrijos also offered unprecedented praise for Carter.

Nevertheless, a spokesman at the U. S. Army headquarters at Quarry Heights said a warning had been issued to U. S. military personnel and their dependents to avoid unneccesary trips out of the Canal Zone Friday. U. S. military police, he added, would be prepared to back up Canal Zone police if any trouble occurs.

Canal Zone police will be on special alert and will monitor such sensitive areas as the Panama City avenues along the Zone and the are around the U. S. Embassy a few miles away.

Since the U. S. and Panamanian negotiating teams announced their agreement here four weeks ago, the government has kept up an intense publicity campaign to obtain wide support for the treaties, which many Panamanians feel fall short of the expectations raised by Torrijos over the years.

The newspapers here published daily accounts of groups that declare their support for the treaties, such as associations of parents, workers, teachers and indigenous people.

The nation's conservative private sector has thus found itself a bedfellow of the Communist Party since both publicly declared the treaties "important steps ahead in the struggle against imperialism."

The press campaign is run largely by a holding company for three government-owned newspapers in which nationalist headlines are daily fare. Matutino, one of these three papers, today carries the headline "The Decolonization Process Has Begun."

In addition to the pro-treaty exhortations in the press and on television, Panama's negotiators and other government spokesmen have travelled the countryside to give briefings on the concessions obtained from the United States.