HANOI, Vietnam — Quietly, Vietnam's Catholic Church is challenging the nation's government more boldly than it ever has since the communists took power over five decades ago.

For several weeks, church leaders and their followers in Hanoi have been gathering daily to pray in front of the old Vatican embassy, one of many church properties taken over by the government after 1954.

The church wants the government to hand back the 2.5-acre lot in central Hanoi, where such land is worth millions of dollars.

"It is a tragedy for us that our holy land was taken away," said Father Nguyen Khac Que, a member of the Hanoi diocese who helped organize the prayer vigils.

Although the dispute could raise church-state tensions, it also offers dramatic testimony to how much church-state relations have improved in Vietnam recently.

Had church leaders dared to make such a public challenge just five years ago, police would almost certainly have jailed them.

"There is now a sufficient feeling of comfort on both sides that the church feels it can air its grievances publicly and the state feels it can tolerate them," said Peter Hansen of the Catholic Theological College in Melbourne, Australia.

Yesterday, the church planned to hold its biggest vigil yet, despite requests from city officials to stop the gatherings.

Hanoi city officials, who control the property, did not respond to requests for interviews.

Church officials say they have documents showing the land belongs to the diocese. But Hanoi officials maintain a former priest voluntarily turned the property over to the government in 1960, according to Duong Ngoc Tan of Vietnam's national Committee for Religious Affairs.

"This whole matter of returning land is very complicated," Tan said.

After the revolution, property was confiscated not just from the church but from wealthy landowners and capitalists. It was then used by the government or turned over to others who have held it for decades.

Church leaders are careful to refer to the gatherings as prayer vigils rather than demonstrations — a loaded word in a country where public protests are generally forbidden.

They are holding vigils at three churches, but the focal point is St. Joseph's — the largest cathedral in Hanoi — which routinely draws up to 2,000 people for services that spill into the courtyard.

During the vigils, hundreds of parishioners at a time gather nearby in front of the old Vatican Embassy, a French-style villa now used as a youth sports center.

During their first vigil, just before Christmas, parishioners wheeled a Virgin Mary statue into the villa, pushing her in a cyclo, a traditional Vietnamese rickshaw. The statue had once sat next to the old embassy but was relocated to the nearby cathedral.

Local authorities have since locked the gate, which parishioners have adorned with white roses. Now the faithful light candles and gather on the sidewalk, occasionally blocking traffic on the narrow street.

On a recent Sunday, a priest carrying a cross led about 500 people to the site, where they prayed, chanted and sang.

There were no uniformed police in sight.

"I could never have imagined doing something like this in the past," said Pham Vu Thuc, 51, a lifelong member of St. Joseph's.

"Things have changed a lot since we've become more connected with the outside world," she said. "We have the Internet, we've joined the World Trade Organization. Now Vietnam has to follow the rules of the international community."

While relations have improved between the church and the national government, Father Que said, conflicts still arise with local governments.

"They once put a discotheque right next to the diocese headquarters," Que said.

Vietnam's Catholic Church, which counts 6 million members, was established by missionaries and grew during French colonial rule in Vietnam. It is the second-largest faith in predominantly Buddhist Vietnam.

Vietnam's Catholic Church has always been regarded with suspicion because of its close relations with the French government and the former South Vietnamese government, which fought a U.S.-backed war against the communists.

For years, Vietnamese Catholics faced persecution, finding it difficult to get jobs or enter universities. Hundreds of thousands fled to southern Vietnam.

Many others stayed behind, and their churches remained open. But the government restricted their activities and took over property next to sanctuaries, including seminaries, schools and medical clinics.

Over time, church-state relations have begun to thaw. Prime Minister Nguyen Tan Dung visited the pope last year, and the two sides have considered restoring diplomatic relations.

The Vietnamese government also approved a new law on religion several years ago that made it easier for unrecognized Protestant faiths to register with the government.

All this has emboldened Catholic leaders.

"We can speak out now," said Father Que. "Things are more democratic now."

Besides, the dispute in Hanoi is not about ideology, Que said. "This is a dispute over valuable land."