On the final night of his visit to Washington in late June, after 15 standing ovations in Congress and an opulent White House dinner tailored to his vegetarian tastes, Prime Minister Narendra Modi of India set time aside to court and be cheered by another important constituency: the Indian diaspora.

Backstage at the Kennedy Center, as business leaders in bespoke suits and fine silk saris filtered into a 1,200-seat theater, Mr. Modi met with a handful of entrepreneurs. Most were young, educated in India, made rich in America, and eager to connect with the man who presents himself as a guru to the world, preaching how this is “the century of India.”

“Thank you for lifting the image and spirits of Indian Americans,” Umesh Sachdev, 37, told the prime minister, explaining that he was the founder of Uniphore, an artificial intelligence business valued at $2.5 billion, with offices in India and California. Mr. Modi tapped Mr. Sachdev’s shoulder and exclaimed “waah,” or wow in Hindi.

With an emphasis on national pride, Mr. Modi and his conservative Hindu-first Bharatiya Janata Party have cultivated a surprisingly strong relationship with India’s successful diaspora. The bond has been strengthened by a global political machine, supercharged under Mr. Modi with party offices in dozens of countries and thousands of volunteers. And it has allowed Mr. Modi to fuse his own image — and his rubric of elevating India — with superstar executives and powerful, often more liberal constituencies in the United States, Britain, Australia and many other nations.

No other world leader seems to draw such a steady flow of diaspora welcome parties, most recently in Paris, New York and Cairo, or giant audiences, including 20,000 fans at a rally in Australia in May. Mr. Modi was in France on Friday as the guest of honor at the annual Bastille Day parade, and with elections next year in India, the pattern has been set.

“The B.J.P. leadership wants to show its strength abroad, to create strength at home,” said Sameer Lalwani, a senior expert on South Asia at the U.S. Institute of Peace.

But in some corners of the diaspora, strains are emerging. Many Indian professionals who cheer when Mr. Modi boasts that India has become the world’s fifth-largest economy — who gush about new infrastructure and more modern cities — also fear that his government’s Hindu-supremacist policies and growing intolerance of scrutiny will keep India from truly standing as a superpower and democratic alternative to China.

Vinod Khosla, a prominent Silicon Valley investor, who has often pushed for closer U.S.-India relations, said in an interview that India’s greatest risk is a disruption to economic growth from the instability and inequality inflamed by Hindu nationalism. Others worry that Mr. Modi, in a bubble of political celebrity and religious certitude, is ignoring the fragility of positive momentum in a complex, diverse and volatile nation of 1.4 billion people.

“The demographics only work for India if there is progressivism and inclusion,” said Arun Subramony, a private equity banker in Washington with digital, health and other investments in India. “The party has to make an extra effort to make clear that India is for everyone.”

The bond between the diaspora and the B.J.P. began with pragmatism — and with the first B.J.P. prime minister, Atal Bihari Vajpayee, who promoted information technology as the solution to India’s development problems in the late 1990s.

Kanwal Rekhi, the first Indian American to take a company public on the Nasdaq, heard Mr. Vajpayee’s speeches and thought: This guy gets it. He asked for a meeting and arrived in New Delhi in April 2000, leading a group called The IndUS Entrepreneurs, or TiE.

At the prime minister’s residence, there were paratroopers on the roof and tanks nearby, vestiges of a recent conflict with Pakistan. Mr. Rekhi was there promising that entrepreneurship could bridge divides — India and Pakistan, Muslims and Hindus. Mr. Vajpayee welcomed their techno-utopianism.

“He asked: ‘What is your sense of India and Indians?’ Then he said, ‘Our future is very bright, and you need to show us the way,’” Mr. Rekhi said in an interview.

So began a relationship with the diaspora that reversed decades of rancor, when those who left with university degrees were seen as traitors to India’s needs. Once Mr. Vajpayee made clear that he saw Indians overseas as guides and consultants, that is what they became.

TiE made several recommendations, bolstered by Stanford professors, and Mr. Vajpayee followed their suggestions. In 2001, for example, his government loosened its monopoly on internet infrastructure, allowing more private competition.

Naren Bakshi, another tech executive in the meetings, recalled that Mr. Vajpayee insisted that the diaspora also play a direct role.

“If you care for India,” he told them, “come to India.”

Mr. Bakshi bought a home near where he had grown up in the state of Rajasthan, and he has spent four months a year in India ever since.

In the early 2000s, he also helped found the India Community Center in Milpitas, Calif., a sprawling complex in a South Asian suburb of San Jose that has become a hub for yoga, Muslim and Hindu holidays, weddings — and, increasingly, meetings with visiting Indian officials.

“People here are very much involved,” Raj Desai, the center’s president, said over tea one recent morning.

In Silicon Valley and elsewhere, Overseas Friends of the B.J.P., the party’s international arm, has become an established presence. Helping with immigration issues and other challenges, its members supplement and compete with India’s understaffed corps of around 950 foreign service officers — a fraction of the roughly 16,000 who work for the United States.

Last year — even though voting in India’s elections must be done in person — the B.J.P. sponsored events with party officials in Texas, New Jersey, Washington, D.C., and North Carolina, as well as several events at the India Community Center in California, according to its mandatory registration filings as a foreign agent.

Visiting officials also bring together smaller groups for dinners and discussion. Mr. Sachdev, the Uniphore chief executive, said he had gone to several such gatherings, adding that the conversations focused on business policy more than politics.

He and other attendees said they had never been asked to contribute to B.J.P. campaigns.

But political scientists believe that the B.J.P. and Hindu organizations draw a significant flow of money from the diaspora. In 2018, Mr. Modi’s government rushed through Parliament a law allowing Indians living abroad and foreign companies with subsidiaries in India to make undisclosed political donations. Spending on India’s 2019 campaign topped $8 billion, making it the most expensive election in the world.

“There’s an absence of transparency, and it’s by design,” said Gilles Verniers, a senior fellow at the Center for Policy Research in New Delhi.

In the United States, the B.J.P. registered its presence — a requirement for any foreign political party — only after questions were raised about the financing of a giant “Howdy Modi” celebration in 2019 in Houston with President Donald J. Trump.

In Australia, the organization still does not appear in the foreign transparency register, despite the costs associated with Mr. Modi’s rally in May at Sydney’s Qudos Bank Arena, where hundreds of people lined up outside for selfies with twin Modi cardboard cutouts framing a giant sign with “We ❤️ Modi” in bright white lights.

“He’s the leader of the century,” said Meera Rawat, after snapping a photo with one of the cardboard Modis.

Her group had reached Sydney on a bus chartered by a local B.J.P. chapter. Several flights were also chartered by the party.

Asked about the process, B.J.P. officials in Australia said everything was “fully funded by the local Indian community and businesses.”

Albel Singh Kang, secretary of the Australian Sikh Association, said his group had initially been recruited for the event. When organizers declined to identify its funders, he passed. Indian Muslim leaders also stayed away, noting that members of Mr. Modi’s party have called for Muslims to be murdered — without strong condemnation from the prime minister.

Many Indians overseas fret about bloodshed in India, where religious minorities make up 20 percent of the population, and where Hindu mobs are regularly accused of lynching people, mostly Muslims, for their food, style of dress, or interfaith marriages. But India’s emigrant families also worry about violence leeching into the countries where they have moved.

In 2021, men armed with bats and hammers attacked four Sikh students in a car in Sydney. After one of the men served a six-month sentence, he returned to India, where he received a hero’s welcome. Tensions among Indian immigrants in Britain, Canada and the United States have also been rising in recent years, along with vandalism and threats.

“The fact is, there are divisions within India, and they are bound to express themselves because politics doesn’t stop at the national shores,” said C. Raja Mohan, a senior fellow with the Asia Society Policy Institute in Delhi.

Rising concerns about polarization are often overlooked amid the Modi pageantry. At the diaspora event in Sydney, Australia’s prime minister, Anthony Albanese, compared Mr. Modi to Bruce Springsteen, calling India’s leader “The Boss,” to huge cheers.

In Washington, where 7,000 Indian Americans joined him in an exuberant celebration on the White House lawn, Mr. Modi said at a news conference that discrimination against minorities did not exist under his government. A few hours later, human rights activists gathered outside the gate, including Muslims who had fled to the United States after facing persecution in India. The TV crews had already moved on.

Behind the scenes, American officials say there has been more nudging of Mr. Modi.

Ro Khanna, co-chair of the Congressional Caucus on India and Indian Americans, who represents the district that includes the India Community Center, said that he had spoken to Mr. Modi about the importance of pluralism.

“I want us to be very much focused on strengthening the U.S.-India relationship under the principle of India’s founding and our founding,” Mr. Khanna said, “and not a celebration of any particular individual.”

Some business leaders say that Mr. Modi deserves their unflagging support. “What’s important to me is, has he been able to put India on a trajectory of growth and global leadership?” said Mr. Sachdev of Uniphore. The United Nations recently reported that India’s economy had lifted 415 million people out of poverty in the past 15 years.

Others have started mixing praise with pragmatic concern. Mr. Khosla, the prominent investor, said it was time to recognize that the government’s favoring of Hindus “can take attention off the principal path of economic progress, and set it back, and set back global relationships.”

Even in Washington’s supportive diaspora crowds, there was a blend of pride and appeals for moderation, for equal opportunity and constructive critique.

Mr. Subramony, the private equity banker, said he grew up in southern India without regular water or electricity, in a compound of 10 families practicing four different religions. He called Mr. Modi “a very quick learner” who would hopefully defend India’s more tolerant values.

“It’s also our responsibility, the people who are feeding Modi, who are being inspired by what is going on in India,” he said. “It is our duty to make him change.”

Sonia Paul contributed reporting from Santa Clara, Calif., and Karan Deep Singh from New Delhi.