The rebels who recently seized power here returned to the impoverished neighborhood that had solidly supported them during the civil war and reaffirmed their intention to create a new economic, political and social structure.

At a rally that ended a two-mile march by 25,000 supporters, leaders of the Sandinista National Directorate, which had led the revolution against dictator Anastasio Somoza, extrolled their two-week-old victory and the society they plan to construct.

Carlos Nuez, one of the speakers, passionately described "the new man and the new Nicaragua we will build."

The rally was called to demonstrate that the Sandinistas retain popular support. It was also designed to keep the anti-Somoza fevor alive as the new government prepares specific policies, some of which are likely to be unpopular, to attain their goal of a socialist economy.

The marchers, most of them from Managu's poorest sections where support for the Sandinistas is greatest, gathered near the Metro Center shopping plaza and made their way to the Don Bosco Youth Center, where the speeches were given.

The carried signs, most of them prepared by Sandinista neighborhood committees with slogans in support of the new junta and against the Somoza government.

The signs also expressed strong opposition to the anti-junta gunmen, probably die-hard members of Somoza's National Guard, who continue to roam the streets at night firing at the young Sandinista soldiers who guard the city.

"Sandinista youths repudiate criminal acts of the remnants of the Somoza dictatorship," one of the signs said. "Repuditiate and punish the counterrevolutionaries," another sign said.

At the Don Bosco center some of the Sandinista speakers concentrated on the corruption and excesses of the old Somoza regime. Others spoke of the problem and sacrifices the Nicaraguan people will have to make to rebuild the country.

"When Somoza was the owner of this country, he gave us the crumbs that he wanted to," Daniel Ortega told the crowd. "When he saw the imminence of his defeat, he took the economy with him in such a way that we found ourselves with an empty house but with a great spirit."

Interspersed with the speeches were the melodic songs of the revolution and chants from the crowd: "Escucha, escucha, estamos en la lucha" a Sandinista battle cry that means, "Listen, listen, we are in the fight!"

The importance the Sandinista leadership attached to the rally was evidence from the way Radio Sandino, the Sandinista-controlled station, has urged its listeners for the past two days to turn out. The march and speeches were broadcast live to the nation today.

The march and rally were held in the heart of the poor eastern barries of Managua, where there was heavy fighting and bombing during the war.

The area is still without water and electricity and is only beginning to clean itself. The site was chosen by the Sandinista leaders to show their interest and concern for the area and the people who live there.

Ortega, in his speech, promised that the problems still facing the eastern section of the city would be resolved soon. He and others also spoke about the agrarian reform, the new army and the new economy the Sandinistas hope to fashion.

The Sandinistas are counting on massive aid from nations and international leading institutions. They have complained that some of the promised food and medicine has been slow in coming and there have been, as yet, few specific announcements of longterm loans.

Today, however, they were promised $225 million in loans from the Inter-American Development Bank, with the first $20 million available immediately.