Deborah Wei first wore a “No Stadium in Chinatown” T-shirt emblazoned with red English letters and Chinese characters in 2000, when she helped to scuttle a proposed baseball stadium for the Phillies.

She wore an updated version a decade later, with the word “Stadium” crossed out and replaced by “Casino,” when local opposition derailed a Foxwoods project.

Now Ms. Wei and other activists are donning a third edition to fight what they fear is the most serious threat yet: a $1.5 billion plan to build a basketball arena for the 76ers, six inches away from Chinatown’s southern boundary.

“I don’t know what is next,” said Ms. Wei, a 66-year-old educator who co-founded the community group Asian Americans United in the 1980s.

Philadelphia, a city that so carefully curates its history, is wrestling over how to shape the future of its storied downtown, which like so many others, saw businesses struggle and disorder spike during the pandemic. And now, with a new mayor about to be sworn in to lead the city of 1.6 million, and a package of legislation related to the Sixers’ arena expected soon, the project is entering a pivotal stretch.

To Chinatown’s champions, the proposed arena fits a pattern of land grabs, paving the way for yet another sports development project. Philadelphia reminds them of what happened in Washington, St. Louis and other cities, when gentrification and redevelopment shrank or erased downtown Chinatowns.

Chinatowns often sprouted in what were the cheapest, least desirable precincts, born of racism and xenophobia. But the same urban enclaves have become so coveted that their longtime inhabitants are being displaced. The National Trust for Historic Preservation named Philadelphia’s Chinatown as one of America’s 11 most endangered historic places in 2023, alongside Seattle’s Chinatown-International District, which faces pressure from a transit project after being squeezed by two sports stadiums.

But to the Sixers, construction unions and some business leaders, the arena promises to create jobs and revitalize an uninviting stretch of downtown Philadelphia, the nation’s poorest big city, that is just a 15-minute walk from Independence Hall and the Liberty Bell.

If the adjacent neighborhoods do not benefit, the project would be a failure, said David J. Adelman, a billionaire part-owner of the 76ers who chairs the 76 DevCo development team. When he was growing up, his family would have Sunday dinners in Chinatown at Riverside restaurant, which has since been replaced by Ocean City. So a sign that graces 10th Street Plaza — “This is, was, will be Chinatown” — feels personal.

“I got the chills the first time I walked by that site,” said Mr. Adelman during an interview at the Wells Fargo Center, the 76ers’ current home, before a game against the Lakers. “I get it. We’re going to do this right. We’re going to honor this and respect this and find a way to enhance.”

The 76ers first proposed the idea in July 2022, and presented the latest version to a contentious city planning panel earlier this month. The city is soon expected to release its own impact assessments, which the Sixers are paying for at the city’s request. That arrangement prompted criticism, but the city said it hired the consultants doing the work “with no input from the Sixers.”

In January, Cherelle Parker will succeed Mayor Jim Kenney, becoming Philadelphia’s first female mayor. While Ms. Parker, a former Democratic state representative and City Council member, has yet to endorse the arena project, the construction unions are among her staunchest supporters.

Ms. Parker told reporters after her November victory that she would prioritize “the community citywide,” not a specific neighborhood, in making a decision.

“You can’t have a project with that potential as it relates to an economic impact and not hear the voices from people in our city,” she said.

Still, the project is hardly a fait accompli, thanks to a potent patchwork of skeptics like urban planners, progressive groups and the city’s biggest corporate titan, Comcast.

The 76ers currently share the Wells Fargo Center with the Flyers; both are owned by Comcast, which also owns NBC Sports Philadelphia, the broadcaster of the Sixers’ home games. The arena is part of a sports and entertainment hub off Interstate 95, where the Eagles and Phillies play, and where the city will host its 2026 World Cup matches.

The Sixers’ lease expires in 2031. In an interview, Daniel J. Hilferty, chairman and chief executive of Comcast Spectacor, the sports and entertainment division, said the company wants the Sixers, who play 41 regular season games at home, to stay put. But Harris Blitzer Sports & Entertainment, the Camden, N.J.-based company that owns the team, has said the Sixers will be gone come 2031.

Instead, they want to be downtown — just like almost every other N.B.A. team — and to control the revenues from games, concerts and other events. Hence the plan for a 18,500-seat arena, three blocks from City Hall.

The current project would not, they stress, mirror the development of Capital One Arena in Washington, the home of the N.B.A.’s Wizards and the N.H.L.’s Capitals. Washington invoked eminent domain to build the arena in 1997, and only 10 percent of the businesses and organizations survived the upheaval. And now, the owner of the Wizards and Capitals wants to move the teams into a new proposed sports district in Alexandria, Va.

“What happened in D.C. was horrible,” Mr. Adelman said in November at a community forum. “Should never have happened and will not happen here.”

Paul R. Levy, the founding chief executive of Center City District, a business improvement organization, expressed hope that the arena would benefit the Market East area, which once boasted half a dozen department stores. Now only Macy’s remains.

“What Market East needs is a massive capital event,” he said.

But Domenic Vitiello, a city planning and urban studies professor at the University of Pennsylvania, said countless studies have concluded that sports projects have not revitalized downtowns or added substantially to cities’ tax bases, relative to the outlay of public subsidies.

“This is the consensus among honest, independent experts — not the consulting firms hired by teams and cities to justify investments that end up harming cities and communities,” said Mr. Vitiello, who has written about the “planned destruction” of Chinatowns in North America.

Surveys have found that over 90 percent of business owners, residents and visitors to Philadelphia’s Chinatown, home to roughly 3,000 people across 20 city blocks, oppose the arena. Among the concerns: traffic congestion, soaring rents, displaced residents and businesses, and the erosion of Chinatown’s cultural character.

Chinatown leaders have organized protests drawing thousands of people and filed dozens of open records requests for communications between the developers and government officials.

During a tour of the arena site, David Gould, chief diversity and impact officer at Harris Blitzer, acknowledged the tensions. But he said he was proud, as a Black Philadelphia native, to partner with a Black-owned firm (which is also backed by a Sixers co-owner) with experience in helping underserved communities.

In Philadelphia, land-use proposals typically require the support of a local council member. For the Sixers’ proposal, that is Mark Squilla, a Democrat elected in 2011. He said he was weighing whether the community could be kept “whole” and protected from “negative impacts.”

“It’s the most lobbied project that I’ve been involved with,” he said.

In Chinatown, murals and plaques abound, memorializing battles over a highway, a prison, a convention center and more, throughout a fraught 150-year history.

What came out of “a history of struggle” was the Folk Arts-Cultural Treasures Charter School, according to the principal, Pheng Lim. Opened in 2005 within the footprint of the Phillies’ aborted stadium, the K-8 school has 500 students from 43 ZIP codes, 64 percent of whom are eligible for free lunch.

“We’re all part of this ecosystem, and the connections are what we’re trying to preserve and protect and fight for,” Ms. Lim said.

Earlier this year, Vancouver hosted a conference for leaders of 18 North American Chinatowns, including Philadelphia’s, examining disruptive developments that “exacerbate the struggle for low-income individuals to find affordable housing.”

Had there been such a conference in the 1960s, St. Louis’s Chinatown, known as Hop Alley, would have been represented.

With 300 people in Hop Alley businesses providing 60 percent of the city’s laundry service, Chinatown “played a huge role economically,” said Huping Ling, a history professor at Truman State University, in Kirksville, Mo.

But the area was turned into a parking lot for Busch Stadium, home of the St. Louis Cardinals — which was demolished in 2005 to make way for another Busch Stadium.

“Chinatown is totally and physically gone,” she said. “It was leveled.”