Pope John Paul II tonight received the most rapturous welcome so far of his return pilgrimage to Poland when he told a mass meeting of Polish youth that the spirit of "solidarity" must never die.

Vast crowds estimated by church officials at more than a million gathered beneath the walls of the medieval monastery of Jasna Gora to hear the pope say he had come to share their suffering. Clapping, singing, and raising their arms above their heads, they created a sense of excitement and enthusiasm that overshadowed the reception he received in Warsaw Thursday.

John Paul's use of the word "solidarity" was taken by his listeners as a deliberate reference to the first independent trade union in the communist world, which emerged from the workers' protest of August 1980 and has since been banned. The pope said that the spirit of solidarity still surrounded "those interned, imprisoned, and dismissed from work."

Waves of applause swept across the sea of humanity as the pope appeared, resplendent in red robes, on the steps of the monastery. The crowd, many of whom were camping out, stretched back for more than a mile from the monastery--considered the holiest place in Poland.

The festivities in Czestochowa, marking the 600th anniversary of the arrival in Poland of a revered religious icon known as the Black Madonna, are the centerpiece of the pope's eight-day pilgrimage. The celebrations were extended after the pope was unable to come to Poland as planned last year because of the imposition of martial law. The thrust of the pope's message to the youths came when he summoned up painful episodes of Poland's 1,000-year history and told them they must be prepared for further sacrifices if they wanted to build a nation.

"Perhaps at times we envy the French, the Germans or the Americans because their name is not tied to such a historical price and because they are much more easily free, while our Polish freedom costs so much."

His voice rising in emotion, he went on: "We do not want a Poland that costs us nothing."

The pope was alternately gentle and magisterial, humorous and solemn with his young listeners. In words that brought tears to the eyes of many in the crowd, he said, "My dear young friends, I love you."

He established an instant personal rapport with his audience, who greeted him by shouting, "The youth is with you" and "Come closer to us, come down here."

The pope, who was sitting on a throne high above the crowd, responded by walking down the steps and standing in front of the altar. There was a roar of "Thank you, thank you" from the pilgrims and the pope asked, "Is there anything else you want?"

"Yes, stay with us, stay longer," the crowd shouted back.

"We have a lot of people from abroad and they will probably think that our Polish youth is too talkative," joked the pope, his voice echoing from loudspeakers away into the distance.

As the bells of the monastery rang out, the pope, now speaking in a soft, solemn voice, expressed the need for "inter-human solidarity."

In the passage on "solidarity," thick with double meaning, the pope said he wanted to "give thanks for all the proofs of this solidarity that have been given by my compatriots, including Polish youth, in the difficult period of not many months ago."

"May this good thing, which appeared in so many places and so many ways, never cease on Polish soil," the pope declared.

Among the banners in the crowd was one signed by the shipyard workers of the Baltic coast whose protests gave birth to Solidarity. Another banner read, "Welcome, John Paul, the defender of human rights."

At the end of the meeting, hundreds of thousands of pilgrims raised their hands in the victory sign as they sang, "Oh, God Who Protects Poland," the anthem of the Polish Roman Catholic Church. They then sang, "May He Live 100 Years" for the pope, a Polish version of "For He's a Jolly Good Fellow."

Heavy reinforcements of police were sent to Czestochowa to keep order in the streets. After the meeting, there was again scattered chanting of pro-Solidarity slogans among young people streaming away from the monastery down the main street of this southern industrial town.

The pope granted a special audience to a group of workers from the northwestern port of Szczecin, another focal point of the workers' rebellion of 1980. In a reference to the outpouring of religious emotion during the strikes, he said the whole world had been amazed by the way in which "the Polish worker stood up for himself with the Gospel in his hand and a prayer on his lips."

"The pictures that went round the world in 1980 touched hearts and consciences," the pope said.

The pontiff was not allowed to visit Gdansk or Szczecin during this pilgrimage, which will, however, take him to such other Solidarity strongholds as Wroclaw, Poznan and Krakow.

The size of the crowds at tonight's meeting with young people and the cold, cloudy weather prompted the pope to joke that the fact that everybody was crammed so tight had the advantage of keeping them warm.

"For the 18th of June, it's not very warm at all. It was much warmer when I was here four years ago, but you are too young to remember," he said. The pilgrims, for whom the pope's first visit to Poland in 1979 was a focal point, shouted back, "We remember, we remember."

"I believe you, I believe you," the pope replied to deafening applause.

Bradley Graham of The Washington Post added from Warsaw:

Before leaving the capital, the pope was driven to the Warsaw Ghetto monument to the 1943 Jewish uprising against the Nazis. Although the visit was not on the formal program, a crowd estimated at 20,000 greeted him there. The pope was said to have requested the added stop.

The pope then traveled by helicopter to the monastic settlement of Niepokalanow outside Warsaw to honor the recently canonized Polish saint, the Rev. Maximilian Kolbe, who volunteered to die in the place of a fellow inmate at the Nazi concentration camp at Auschwitz.

In a homily before a throng of people with umbrellas opened against the cool drizzle, John Paul II raised his voice to bellow the words of St. Paul. "Do not be overcome by evil, but overcome evil with good," he said.

Repeating this phrase a few minutes later, the pope said it represented "the program of the gospel," which is difficult but possible and indispensable. His statement, greeted with applause by the crowd filled with many farmers once belonging to the outlawed Rural Solidarity union, was interpreted as a papal lesson in nonviolent resistance and constructive action.

In a message directed explicitly at Polish farmers, the pope underscored the development of "pastoral communities" in the countryside. A number of former Rural Solidarity activists have turned to these religious groups as an alternate outlet, a fact that could become a source of church-state friction.

Much of the homily was devoted to praise of Kolbe, who founded the settlement of Niepokalanow (meaning "the immaculate") in 1927. John Paul II described him not only as a martyr but also as a fellow countryman and first Polish saint of the second millennium.

Moving to establish Kolbe as a modern-day symbol of Polish and Christian suffering, the pope declared: "Since he is a son of this land, one who shared in its trials, its sufferings and its hopes, therefore, in a certain special way, he is the patron of Poland."

He avoided mention of a recent church-state clash involving Kolbe's past, begun when government spokesman Jerzy Urban--who was later defended by Deputy Premier Mieczyslaw Rakowski--made a slighting reference to the anti-Semitism in two publications by Kolbe that circulated between the two world wars. At that time, there was a considerable campaign against Jews by nationalists, large landholders and elements of the Roman Catholic Church.