Across India, the anti-Christian forces are growing stronger by the day, and they have many faces, including a white-collar army of lawyers and clerks who file legal complaints against Christian organizations. They also devise devastating social boycotts against isolated Christians in remote villages. According to extensive interviews, Hindu nationalists have blocked Christians from community wells, barred them from visiting Hindu homes and ostracized villagers for believing in Jesus. Last year, in one town, they stopped people from gathering on Christmas.

INDORE, India — The Christians were mid-hymn when the mob kicked in the door.

A swarm of men dressed in saffron poured inside. They jumped onstage and shouted Hindu supremacist slogans. They punched pastors in the head. They threw women to the ground, sending terrified children scuttling under their chairs.

“They kept beating us, pulling out hair,” said Manish David, one of the pastors who was assaulted. “They yelled: ‘What are you doing here? What songs are you singing? What are you trying to do?’”

The attack unfolded on the morning of Jan. 26 at the Satprakashan Sanchar Kendra Christian center in the city of Indore. The police soon arrived, but the officers did not touch the aggressors. Instead, they arrested and jailed the pastors and other church elders, who were still dizzy from getting punched in the head. The Christians were charged with breaking a newly enforced law that targets religious conversions, one that mirrors at least a dozen other measures across the country that have prompted a surge in mob violence against Indian Christians.

Pastor David was not converting anyone, he said. But the organized assault against his church was propelled by a growing anti-Christian hysteria that is spreading across this vast nation, home to one of Asia’s oldest and largest Christian communities, with more than 30 million adherents.

Anti-Christian vigilantes are sweeping through villages, storming churches, burning Christian literature, attacking schools and assaulting worshipers. In many cases, the police and members of India’s governing party are helping them, government documents and dozens of interviews revealed. In church after church, the very act of worship has become dangerous despite constitutional protections for freedom of religion.

To many Hindu extremists, the attacks are justified — a means of preventing religious conversions. To them, the possibility that some Indians, even a relatively small number, would reject Hinduism for Christianity is a threat to their dream of turning India into a pure Hindu nation. Many Christians have become so frightened that they try to pass as Hindu to protect themselves.

“I just don’t get it,” said Abhishek Ninama, a Christian farmer, who stared dejectedly at a rural church stomped apart this year. “What is it that we do that makes them hate us so much?”

The pressure is greatest in central and northern India, where the governing party of Prime Minister Narendra Modi is firmly in control, and where evangelical Christian groups are making inroads among lower-caste Hindus, albeit quietly. Pastors hold clandestine ceremonies at night. They conduct secret baptisms. They pass out audio Bibles that look like little transistor radios so that illiterate farmers can surreptitiously listen to the scripture as they plow their fields.

Since its independence in 1947, India has been the world’s largest experiment in democracy. At times, communal violence, often between Hindus and Muslims, has tested its commitment to religious pluralism, but usually the authorities try, albeit sometimes too slowly, to tamp it down.

The issue of conversions to Christianity from Hinduism is an especially touchy subject, one that has vexed the country for years and even drew in Jawaharlal Nehru, India’s first prime minister, who fiercely guarded India’s secular ideals. In the past few years, Mr. Modi and his Hindu nationalist party have tugged India far to the right, away from what many Indians see as the multicultural foundation Nehru built. The rising attacks on Christians, who make up about 2 percent of the population, are part of a broader shift in India, in which minorities feel less safe.

Mr. Modi is facing increasing international pressure to rein in his supporters and stop the persecution of Muslims and Christians. The United States Commission on International Religious Freedom, a government body, recommended that India be put on its red list for “severe violations of religious freedom” — a charge the Modi administration strongly denied.

But across India, the anti-Christian forces are growing stronger by the day, and they have many faces, including a white-collar army of lawyers and clerks who file legal complaints against Christian organizations. They also devise devastating social boycotts against isolated Christians in remote villages. According to extensive interviews, Hindu nationalists have blocked Christians from community wells, barred them from visiting Hindu homes and ostracized villagers for believing in Jesus. Last year, in one town, they stopped people from gathering on Christmas.

“Christians are being suppressed, discriminated against and persecuted at rising levels like never before in India,” said Matias Perttula, the advocacy director at International Christian Concern, a leading anti-persecution group. “And the attackers run free, every time.”

“They Want to Remove Us From Society”

Dilip Chouhan sits in an office behind a copy shop in the small central Indian town of Alirajpur, meaty arms folded across his chest. Above him stretches a poster of a tribal warrior. Mr. Chouhan is part of a growing network of anti-Christian muscle.

Just the mention of Christians makes his face pucker, as if he licked a lemon.

“These ‘believers,’” he said, using the term derisively, “they promise all kinds of stuff — motorcycles, TVs, fridges. They work off superstition. They mislead people.”

Mr. Chouhan lives in the central state of Madhya Pradesh, which this year passed an anti-conversion law that carries prison sentences of up to 10 years for any person found guilty of leading illegal conversions, which are vaguely defined. Energized by this law, Mr. Chouhan, 35, and scores of other young Hindu nationalists have stormed a string of churches. Some of the raids were broadcast on the news, including footage of Mr. Chouhan barging into one church with a shotgun on his back.

He said he wore the gun on his back simply out of “fashion,” and a senior police officer in that area said there would be no charges. Instead, as happened with the Indore episode, several pastors in the ransacked churches were jailed on charges of illegal conversions. Police officials declined to share their evidence.

Mr. Chouhan says his group, which uses WhatsApp to plan its raids on upcoming church services, has 5,000 members. It is part of a constellation of Hindu nationalist organizations across the country, including the Rashtriya Swayamsevak Sangh, or R.S.S., as well as many members of Mr. Modi’s Bharatiya Janata Party, or the B.J.P.

“The B.J.P. is really into this issue, big time,” said Gaurav Tiwari, a party youth leader in Madhya Pradesh.