A REALLY interesting article from the October 5 NY Times magazine. Magazine articles tend to be long, so get comfortable enough for five pages on the most likely demographic future of the country.

The building at 59-21 Calloway Street in Corona, Queens, is grandly named the Calloway Chateau, but it is really the 21st-century version of Ludlow Street, the first stop off the long-haul plane from Bukhara or Bombay. You put your bags down here, a half-hour's drive on the Grand Central Parkway from J.F.K., and pause to gather breath for the journey into the hinterland.

The residents of the Calloway Chateau are brown, white, black and olive; Jewish, Catholic, Protestant, Russian Orthodox, Muslim, Hindu, Sikh, Buddhist. Joseph Salvo, director of the population division at the City Planning Office, calls what's happening in Queens ''probably the greatest social experiment in history.'' It is the most ethnically diverse county in the country. In 1990, there were 243 census tracts in Queens County that were predominantly white; by 2000, the number had dropped to 116. For the past 10 years, Salvo, along with two colleagues, Arun Peter Lobo and Ronald Flores, has been charting with great specificity where different ethnic groups settle in New York. They have found that there are an increasing number of areas, dubbed ''melting-pot tracts,'' in which no single group dominates. The bar for being classified a melting-pot tract is high: there must be three separate groups who account for at least 20 percent of the population. Between 1990 and 2000, the number of melting-pot tracts in the city rose from 64 to 84. More than half of them are in Queens.

The Calloway Chateau is in Tract 437, in Corona. The tract is Hispanic-dominated as a whole (it is 52 percent Hispanic), but it is also significantly white, Asian and black. The number of people in Tract 437 who identify their ancestry as ''United States or American'' (173) are outnumbered by those who list their ancestry as ''sub-Saharan African'' (199). ''Then you break it up by block,'' Salvo says, ''and you got the U.N. in there.''

Five of the blocks within the tract have been classified as melting-pot blocks. One of those is Calloway Street. Of the 907 residents of the block, 29 percent are Hispanic, 23 percent are white, 23 percent are Asian and 19 percent are black. ''This is extraordinary,'' Salvo says, even for Queens. ''These percentages are not typical.''

Despite this astounding diversity, groups tend to stay within enclaves in the borough; even in mixed blocks, one group or another predominates in each individual building. When I read out the list of nationalities residing in the Calloway Chateau -- Uzbeks, Afghans, Indians, Pakistanis, Bangladeshis, Koreans, Filipinos, Ukrainians, Russians, Argentines, Colombians, Dominicans, Puerto Ricans, Peruvians, African-Americans, Guyanese -- Salvo draws in his breath. ''If you look at this building relative to all the buildings in Queens, this is going to stand out. Here is a rather extraordinary example of the melting-pot concept.'' While the Census Bureau doesn't compile data at the level of the individual building, it is quite possible that, for its size, the Calloway Chateau is the most diverse building in New York City.