At least three and possibly as many as seven persons were trampled to death and scores of others injured early this morning as tens of thousands of people tried to force their way into a soccer stadium here where Pope John II was due to see local folk dancers and musicians perform in his honor.

It was the first tragedy to mar John Paul's 10-day visit to Brazil, where vast crowds have turned out each day in cities throughout the country to catch a glimpse of him. He is the first pope to visit the world's most populous Catholic nation, and despite generally chaotic conditions and poor planning on the part Brazilian authorities, there had not been a single reported injury until today.

According to Gen. Assis Bezerra, chief to military security in Fortaleza, in the incident occurred about 4 a.m. when several of the stadium's gates were forced open by an estimated 100,000 persons who had gathered in front of Castelao Stadium. The crowds, many without tickets, surged through the open gates, trampling to death at least three women who either lost their balance or were pushed by those behind them.

The stadium had been scheduled to open at 8 a.m., about three hours before John Paul's arrival.

Bezerra said in an official statement that in addition to three confirmed deaths, 31 others were injured during the stampede. Later in the day, unofficial police reports raised the number of deaths to seven while local hospital's reported that more than 100 persons had been admitted with injuries suffered during the incident.

A similar incident occurred May 4 as the pope celebrated mass in a stadium in Kinshara, Zaire. Nine persons were trampled when crowds rushed a gate to see the pontiff.

Gov. Virgilio Tavora attributed the tragedy to "an excess of enthusiasm" on the part of the people of Fortaleza, the 11th city the pope has visited since his arrival in Brazil June 30. The pope's principal reason for coming here was to open the National Eucharistic Conference, celebrated every five years by Brazil's 335 bishops.

Despite this morning's incident, the pope attended the folk music show as scheduled, celebrated a customary open-air mass and then opened the bishops' conference. This year the conference will examine the plight of the millions of Brazilians who have moved within the country or emigrated to seek better economic opportunities.

The greatest migration has occurred between the country's impoverished northeast, where Fortaleza is located, to the more prosperous industrialized areas in southern Brazil, such as Rio de Janeior and Sao Paulo. The declining northeast, once Brazil's most prosperous sugar and cotton growing area, is plagued by droughts and floods and receives little aid from the federal government compared to the resources lavished on the major population centers to the south.

Some Brazilian bishops in the northeast, Such as Dom Helder Camara of Recife and Aloisio Cardinal Lorscheider of Fortaleza contend that Brazil's military government has deliberately encouraged this migration to provide a steady and cheap labor pool for the large multinational corporations that have built huge factories in and around Sao Paulo.

The church believes the government cares less about the poor than about the country's industrial growth, which numerous studies have shown benefits only about 25 percent of Brazil's 120 million people. The rest, these studies show, continue to live at or below the poverty level.

In an address prepared for the Eucharistic Conference, Lorscheider said, "This move from one place to another if there were not behind it another origin, another cause.

"Behind it there is almost always an injustice, a misery, a brother expoiting another brother, a brother making impossible the life of another brother . . . A pressure that forces that compels the other to leave, to part," he said.

In his opening remarks to the Eucharistic Conference today, John Paul described what he termed the "broad and complex" economic and social forces that have led to the migrations from north to south Brazil, as well as the "unhappiness and solitude" of those forced to leave their homes and families in the northeast for the often difficult life in cities such as Sao Paulo.

"In this complex situation, there is cultural and sometimes linguistic alienation, there is temporary or permanent separation of families, there are the difficulties of integration into a new environment, there is socio-'poltical disequilibrium," the pope told the assembled bishops. His address was broadcast throughout most of Brazil.

"The church cannot refrain from denouncing situations that constrain the many who migrate." the pope said, implicitly supporting the church in its disputes with the Brazilian government over social and economic policy.

"It is necessary that the church confirm its denunciations by concrete pastoral action," the pontiff added in a clear reference to the Brazilian church's recent support for labor union strikes and for small farmers whose lands are being expropriated by large agro-businessnes.