Pope John Paul II received a joyous welcome this afternoon as millions of this city's residents crowded the route from Galeao Airport to the monument of Dos Pracinhas, where the pope celebrated mass before crowds of hundreds of thousands of people. Church bells ring throughout the city at 4:40 p.m., the moment his plane touched down.

The enthusiasm here was far more evident than it was yesterday in Brasilia, where the pope began his 12-day visit to Brazil. The crowds today waved flags, shouted and sang as the pope passed before them. The pontiff seemed more rested and enthusiastic than he had been after arriving in Brazil's capital city after an exhausting 12-hour flight from Rome.

The pope's first words after climbing to the huge altar from which he celebrated mass here today were, "Great is my joy to meet with the people of Rio De Janeiro."

The homily here contained strong language to urge Brazil to adopt policies aimed at eradicating poverty and securing social justice for the tens of millions in this country who have been left out of its economic "miracle."

Earlier today in Belo Horizonte, where the pope celebrated mass before traveling to Rio, John Paul delivered a homily dedicated to this country's youth. Half of Brazil's population of 120 million is younger than 25.

"The greatest riches of this immensely rich country are you yourselves," John Paul told an estimated crowd of 2 million in Belo Horizonte, the size of which Vatican observers compared to the crowds that greeted the pope last year in Mexico. "The real future of this country . . . is found in you. And so this country and with it the church look to [youth] with a look of expectation and hope."

"Don't be led astray by the exasperation of sex which tears down the authenticity of human love and leads to the breakup of the family," the pontiff said. "Overcome the temptation of the so-called consumer society. Strive for austerity and frugality. Otherwise you will slip around like bubbles of soap."

The pope recalled his own youth in Poland during World War II. "You are resolved to construct a just, free and prosperous society where each and everyone can reap the fruits of progress."

"In my youth, I myself lived these convictions. I declaimed them, as a young student . . . God wanted that they received their temper of fire in a war whose atrocity did not spare my home. I saw these convictions trampled on in so many ways," the pope said.

Most observers here believe that John Paul already has demonstrated in his remarks so far that he finally supports the Brazilian church's liberal stand in favor of the poor and dispossessed. The church here has been active in efforts to secure rights for workers and landless peasants. These efforts have led to deep antagonisms between the country's right-wing military leaders and the church.

Last night, the pope warned the government leaders assembled in Brasilia that "those who are responsible for the common good, particularly those who consider themselves Christians, must seek in time the reforms" necessary to avoid revolutionary "currents" that lead to violence and repression of human rights by right or left-wing dictatorships.

The church, the pope said, "can only look with satisfaction upon those efforts that help safeguard and promote fundamental rights and liberties for all human beings and ensure their participation in community and social life.