Pope John Paul II arrived in Mexico today and was greeted by a mariachi band, a gift sombrero and a jubilant crowd estimated at more than 1 million.

Huge crowds lined virtually every inch of the 10-mile route traveled by the papal motorcade from the airport to the Metropolitan Cathedral. Many tossed flowers and candies into the converted open-topped bus in which the smiling pope stood waving.

Speculation as to how the Mexican government, which outlawed church-state relations in the early part of this century, would receive John Paul was ended when President Jose Lopez Portillo appeared at the airport to welcome him. Mexican anti-clerics have strongly critizied the pope's visit.

Offering a handshake rather than the usual Latin embrace, Lopez Portillo wished the pope success in his travels to four other Mexican cities over the next five days.

"I leave you in the hands of the hierarchy and the faithful of your church," Lopez Portillo said in a brief statement, "and may everything be for the good of humanity."

Lopez Portillo, accompanied only by his wife and an aide, then disappeared into his limousine while the pontiff was immediately surrounded by a crush of photographers, reporters and Latin American clergy here for the third Latin American Bishops' Conference that the pope will open Sunday in the city of Puebla.

The pope faces the challenge at the conference of showing they way to the Latin bishops sharply divided on their role in the region's troubled societies.

In the Dominican Republic, the first stop on the pope's week-long trip -- the first in his 3-month-old term -- the crowds were large. But the Mexican crowds were larger and much more boisterous than the well-behaved Dominicans. At the same time, while the Dominican government welcomed him with a 21-gun salute the welcome here, except for Lopez Portillo's brief visit, was pointedly secular.

The 1917 Mexican constitution, in reaction to the enormous political power once wielded by the Catholic Church here, outlawed church schools, expropriated church property, established penalties for church involvement in politics and prohibited the wearing of clerical dress in public.

Since more than 90 percent of Mexico's 65 million people are practicing Catholics, the government years ago arrived at a tacit agreement to turn its head at many church activities as long as the church stayed out of politics.

John Paul technically broke the law here by his public appearance in vestments and by his brief public speech in the Zocalo central square

As in Santo Domingo, the pope knelt to kiss the ground when he stepped down from a special plane, sent to the Dominican Republic by the Mexican government.

Quickly surrounded, the pope tried to make his way to viewing stands on the runway from which tens of thousands of Mexican chanted, "Get out, press." At one point, while a mariachi band played "Cielito Lindo," someone in the crowd handed John Paul a huge sombrero which he briefly placed on top of his head.

Anticipation over the pope's arrival reached fever pitch long before the plane touched down. Three sharp earth tremors failed to faze the gathering crowds, nor did a fourth one after the pope's arrival into this city of more than 8 million inhabitants.

Color photos of the pontiff, sold for several dollars apiece, adorned homes, shops and car windows. Live television coverage began with the Santo Domingo stop and virtually every newspaper devoted its front page to stories chronicling every aspect of the trip -- from what he ate for lunch to how many hads he shook.

One newspaper humorist summed up the atmosphere with an affectionately satirical column describing a rural farmer's attempt to get a priest or reporter to visit his 46-year-old daughter -- a virgin, he said, who had just given birth. They were all too busy watching the pope on television.

Most downtown subway stops were closed for the day, as were many of the city's thoroughfares. The Mexico City police chief issued a public appeal to parents not to bring their children to see the pope for fear they would be lost or crushed by the crowd.

Before leaving Santo Domingo early this morning, the pope spoke to tens of thousands of Dominicans from a balcony at the Children's Hospital in Las Minas, the city's largest slum.

Departing from his prepared speech in Spanish, he told them "since this trip was planned. I wanted to come to Las Minas, to visit you, the poor."

While the crowd chanted "Juan Pablo, Juan Pablo," the pontiff grinned and shouted over then, "Jesu Cristo, Jesu Cristo." Seemingly caught up in the emotion and wanting to respond in kind, he spread his arms and shouted to cheers and applause, "long live youth -- they are out hope."

On several occasions, he broke with his schedule and stopped his caravan to shake hands, kiss babies and give blessings.

While there is no doubt of John Paul II's popularity with the faithful, the more than 350 delegates to the Latin American Bishops' Conference he will open this weekend are still nervously waiting to see what message he has for them.

Ten years after their last conference, in Medellin, Colombia, where Pope Paul VI instructed them to "persevere in facing, with broad and courageous vision, the reforms necessary for a more just and efficient Social arrangement" in Latin America, the Latin church is still arguing about how to do just that.

In those 10 years, the situation has become, if anything, even more extreme. Rightist or military governments control all but a half dozen Latin American countries. Social and economic inequalities have increased.

By some estimates, more than 800 priests in Latin America have been killed arrested, tortured, deported or exiled over the past decade. Most of them have been accused of subversive activity ranging from criticism of human rights violations to participation in guerrilla groups.

While a few priests have changed their cassocks for guns -- a Spanish priest was killed in Nicaragua last November while participating in an armed guerrilla raid -- the majority of those persecuted owe their problems to more mundane forms of activism, like preaching a doctrine of social justice.

Their goal, and the goal of many less militant clerics, is to raise the church out of its traditional torpor and support of those with money and power through grass-roots organization of the poor -- to varying degrees they have taken Medellin at its word.

Other sectors within the church, however, have reacted strongly against any church participation in what is construed as politics.

The controversy has become so heated in recent years that it is common for the more militant on both sides to refer to their opposites as either Marxists or CIA agents.

Both the extremists and the large majority in the middle are waiting for John Paul to give them direction. In three months on the papal throne, he has given little indication of where he stands. While he has spoken strongly in favor of human rights, he has adopted a conservative approach on the question of how individual priests and the church as a whole should conduct themselves.

The new pope has criticized the "destructive and joyless" consumer society of capitalism but, based primarily on his experiences in Poland, is a strong anticommunist.

In a homily during today's cathedral mass, John Paul gave few clues as to what he will say at Puebla, and his statement appeared somewhat contradictory. While he warned those who mistakenly speak in terms of the "new church," he called on the faithful to practice their creed in the face of "fear, fatigue and insecurity," no matter what the consequences.

It will be at Puebla, the Latin American Catholic clergy believes, that they will find out what kind of a pope John Paul is.