Tens of thousands of members of a Buddhist-based spiritual movement staged anti-government demonstrations in 30 cities across China today to demand the immediate release of jailed group leaders, according to protesters and a Hong Kong-based human rights group.

The demonstrations were the most widespread and broad-based since the massive democracy rallies of 10 years ago, and squads of riot-equipped police moved against the hundreds of protesters here in the capital -- most of them middle-aged -- as they tried to gather outside Communist Party headquarters.

Many of the Beijing demonstrators were summarily arrested and hauled away in vans to detention areas set up in parking lots at two sports stadiums on the outskirts of the city, relatives said. "They just dragged them to the bus and took them to the stadium," said one.

The group involved, Falun Gong, or Wheel of the Law, was founded in 1992 by a former Chinese soldier named Li Hongzhi, who now lives in the United States. It combines Buddhist teachings and other traditional Chinese principles with meditation and martial arts discipline as a prescription for physical and spiritual well-being.

It is not entirely clear why Beijing authorities decided to move against Falun Gong, but analysts note that the group's large and growing membership -- estimated at between 10 million and 60 million -- and its apparent capacity to bring large numbers of highly motivated people into the street quickly could be viewed as a potential threat to government security.

It is also unclear if any political motivation lies behind the movement, and this apparent absence of ideology has complicated Beijing's response to it. Unlike the recently banned China Democracy Party, which advocates democratic reform, Falun Gong was a less obvious target, and the government had avoided confronting it for fear of alienating the hundreds of millions of Chinese who believe in some form of qigong -- the practice of directing energy through one's body, which serves as the basis of much of the group's teachings.

But authorities were jolted into action in April, when more than 10,000 Falun Gong members nearly surrounded the Communist Party and government leadership compound in Beijing in a silent demand for legal status for their group. The demonstration was peaceful, and participants cleaned up their own trash before they filed away at the end of the day.

The government has closely monitored the group ever since, and this month it launched a crackdown that resulted in the detention of an estimated 70 Falun Gong leaders, including Li Chang, who had represented the group in previous discussions with the government.

Today's demonstrations here and in other major Chinese cities were organized to protest those arrests. In the southern city of Guangzhou, several thousand Falun Gong members gathered outside government offices, while about 1,000 others protested in the neighboring city of Shenzhen, according to participants and the Hong Kong-based Information Center of Human Rights and Democratic Movement in China.

In Shanghai, police isolated several hundred protesters who had gathered in a square across from city hall but did not move immediately to make arrests, while in the southwestern provincial capital of Guiyang government officials met with protest leaders in an apparent effort to reduce tensions.

While many details of the nationwide protest remain sketchy, its breadth illustrates how deeply Falun Gong reaches into Chinese society, and the challenge such a movement could present to China's Communist rulers. Indeed, several of the group's top leaders are, or were, senior officials in local police, army and security units.

For the past two centuries, Chinese society has been a wellspring of home-grown sects, spiritual movements and particularist causes -- such as the Taipings of the mid-19th century, who were led by a former school teacher who believed he was the younger brother of Jesus, and the xenophobic Boxers of the early 20th century. Both groups were sustained by a population willing to embrace a sometimes bizarre spirituality as a solution to their difficult lives.

Like the Taipings and the Boxers, many of Falun Gong's members are unemployed or retired workers, underprivileged farmers or others with little hope of prosperity who have embraced the group as an escape. Groups like Falun Gong cater to the millions of people who have not benefited from China's economic surge, or who feel they have been cast adrift amid the changes jarring Chinese society.

One typical member, retired primary school teacher Sun Lixia, 58, said Falun Gong "does nothing at all to harm anyone, or society. We want to be recognized." But in an example of just the kind of devotion that disturbs Chinese leaders, she pointed to a picture she carries of Falun Gong founder Li Hongzhi and said: "Our master is in America."

Like Sun, Falun Gong members have an intense reverence for "master" Li, who fled into exile in 1998 after Chinese security began to pay closer attention to his activities. Dog-eared copies of Li's writings, which hold that cultivating an "orb of energy" in one's belly will lead to enlightenment, are staples at early-morning breathing drills staged by Falun Gong adherents in parks around the country.

CAPTION: Falun Gong members meditate and read spiritual works outside the Chinese Embassy in Washington in solidarity with movement protesters in China.

CAPTION: Police at Communist Party headquarters in Beijing round up women who protested the detention of the leaders of the Falun Gong movement.