NEW YORK » He grew up playing in the narrow, crowded streets of Manhattan's Chinatown. He has lived and worked there for all his 61 years. But as Wee Wong walks the neighborhood these days, he cannot understand half the Chinese conversations he hears.

Cantonese, a dialect from southern China that has dominated the Chinatowns of North America for decades, is being rapidly swept aside by Mandarin, the national language of China and the lingua franca of most of the latest Chinese immigrants.

The change can be heard in the neighborhood's lively restaurants and solemn church services, in parks, street markets and language schools. It has been accelerated by Chinese-American parents, including many who speak Cantonese at home, as they press their children to learn Mandarin for the advantages it could bring as China's influence grows in the world.

But the eclipse of Cantonese — in New York, China and around the world — has become a challenge for older people who speak only that dialect and face increasing isolation unless they learn Mandarin or English. Though Cantonese and Mandarin share nearly all the same written characters, the pronunciations are vastly different; when spoken, Mandarin may be incomprehensible to a Cantonese speaker, and vice versa.

Wong, a retired sign maker who speaks English, can still get by with his Cantonese, which remains the preferred language in his circle of friends and in Chinatown's historic core. A bit defiantly, he said that if he enters a shop and finds the staff does not speak his dialect, “;I go to another store.”;

Like many others, however, he is resigned to the likelihood that Cantonese — and the people who speak it — will soon become just another facet of a polyglot neighborhood. “;In 10 years,”; Wong said, “;it will be totally different.”;

With Mandarin's ascent has come a realignment of power in Chinese-American communities, where the recent immigrants are gaining economic and political clout, said Peter Kwong, a professor of Asian-American studies at Hunter College.

“;The fact of the matter is that you have a whole generation switch, with very few people speaking only Cantonese,”; he said. The Cantonese-speaking populace, he added, “;is not the player anymore.”;

The switch mirrors a sea change under way in China, where Mandarin, as the official language, is becoming the default tongue everywhere.

In North America, its rise also reflects a major shift in immigration. For much of the last century, most Chinese living in the United States and Canada traced their ancestry to a region in the Pearl River Delta that included the district of Taishan. They spoke the Taishanese dialect, which is derived from and somewhat similar to Cantonese.

Immigration reform in 1965 opened the door to a huge influx of Cantonese speakers from Hong Kong, and Cantonese became the dominant tongue. But since the 1990s, the vast majority of new Chinese immigrants have come from mainland China, especially Fujian province, and tend to speak Mandarin along with their regional dialects.

In New York, many Mandarin speakers have flocked to Sunset Park, Brooklyn, and Flushing, Queens, which now rivals Chinatown as a center of Chinese-American business and political might, as well as culture and cuisine. In Chinatown, most of the newer immigrants have settled outside the historic core west of the Bowery, clustering instead around East Broadway.

“;I can't even order food on East Broadway,”; said Jan Lee, 44, a furniture designer who has lived all his life in Chinatown and speaks Cantonese. “;They don't speak English; I don't speak Mandarin. I'm just as lost as everyone else.”;

Now Mandarin is pushing into Chinatown's heart.

For most of the 100 years that the New York Chinese School, on Mott Street, has offered language classes, nearly all have taught Cantonese. Last year, the numbers of Cantonese and Mandarin classes were roughly equal. And this year, Mandarin classes outnumber Cantonese 3 to 1, even though most students are from homes where Cantonese is spoken, said the principal, Kin S. Wong.

Some Cantonese-speaking parents are deciding it is more important to point their children toward the future than the past — their family's native dialect — even if that leaves them unable to communicate well with relatives in China.

“;I figure if they have to acquire a language, I wanted them to have Mandarin because it makes it easier when they go into the workplace,”; said Jennifer Ng, whose 5-year-old daughter studies Mandarin at the language school of the Church of the Transfiguration, a Roman Catholic parish on Mott Street where nearly half the classes are devoted to Mandarin. Her 8-year-old son takes Cantonese, but only because there is no English-speaking Mandarin teacher for his age group.

“;Can I tell you the truth?”; she said. “;They hate it! But it's important for the future.”;

Until recently, Sunday Masses at Transfiguration were said in Cantonese. The church now offers two in Mandarin and only one in Cantonese. And as the arrivals from mainland China become old-timers, “;we are beginning to have Mandarin funerals,”; said the Rev. Raymond Nobiletti, the Cantonese-speaking pastor.

At the Chinese Consolidated Benevolent Association, which has been the unofficial government of Chinatown for generations and conducts its business in Cantonese, the president, Justin Yu, said he was the first whose mother tongue was Mandarin to lead the 126-year-old organization. Though he has been taking Cantonese lessons in order to keep up at association meetings, his pronunciation is sometimes a source of hilarity for his colleagues, he said.

“;No matter what,”; he added, laughing, “;you have to admire my courage.”;

But even Yu's association is being surpassed in influence by Fujianese organizations, said Kwong of Hunter College.

Longtime residents seem less threatened than wistful. Though he is known around Chinatown for what he calls his “;legendarily bad”; Cantonese, Paul Lee, 59, said it pained him that the dialect was disappearing from the place where his family has lived for more than a century.

“;It may be a dying language,”; he acknowledged. “;I just hate to say that.”;

But he pointed out that the changes were a natural part of an evolving immigrant neighborhood: Just as Cantonese sidelined Taishanese, so, too, is Mandarin replacing Cantonese.

Wong, the principal of the New York Chinese School, said he had tried to adjust to the subtle shifts during his 40 years in Chinatown. When he arrived in 1969, he walked into a coffee shop and placed his order in Cantonese. Other patrons looked at him oddly.

“;They said, 'Where you from?”;' he recalled. “;'Why you speak Cantonese?”;' They were from Taishan, he said, so he switched to Taishanese and everyone was happy.

“;And now I speak Mandarin better than Cantonese,”; he added with a chuckle. “;So, Chinatown — it's always changing.”;