300,000,000: estimated population of the United States in October 2006

Sam Roberts:

As of yesterday, the Census Bureau officially pegged the resident population of the United States at closing in on 297,900,000. The bureau estimates that with a baby being born every 8 seconds, someone dying every 12 seconds and the nation gaining an immigrant every 31 seconds on average, the population is growing by one person every 14 seconds.

At that rate, the total is expected to top 300 million late this year. But with those projections adjusted monthly and the number of births typically peaking during the summer, the benchmark is likely to be reached about nine months from now.

"You end up with a number in October," said Katrina Wengert, a demographer and a keeper of the Census Bureau's official Population Clock, getting about as specific as possible this far in advance in a field subject to chronic fudging and revising. The clock is, itself, a contrivance, of course, but no more so than other pretexts for a wintertime sexual encounter. Rest assured that hospital publicists, canny obstetricians, entrepreneurial chambers of commerce, baby food manufacturers, public officials and countless others pursuing some political social or personal agenda, abetted by the media, are already guesstimating the growth rate to anoint any number of unsuspecting newborns as the mythical American who pushed the nation's population to 300 million.

In 1967, when the population reached 200 million, Life magazine dispatched 23 photographers to locate the baby and devoted a five-page spread to its search. Instead of deciding on a statistically valid symbol of the average American newborn, the magazine chose the one born at precisely the appointed time.

Life immortalized Robert Ken Woo Jr. of Atlanta, whose parents, a computer programmer and a chemical engineer, had immigrated seven years earlier from China. Mr. Woo graduated magna cum laude from Harvard and is a litigator. Now 38, he still lives in Atlanta with his wife, Angie, who is also a lawyer, and their three daughters.

"He did feel an obligation to do well," Ms. Woo said. "But I think he would have done well, regardless."

This time, like last, the selection is subject to all manner of qualifications, not the least of which is the conceit that the census can measure individuals so precisely as to determine the exact time that the population tops 300 million or, playing the odds, can define the average American newborn.

Still, demographers do know that the United States, which ranks third in population behind China and India, is still gaining people while many other industrialized nations are not. (Japan, officials there announced last month, has begun shrinking.) Driven by immigration and higher fertility rates, particularly among newcomers from abroad, the United States' population is growing by just under 1 percent annually, the equivalent of the entire population of Chicago (2.8 million).

Given the demographic changes recorded in the 20th century, the 300 millionth American, born in the same year the first baby boomers turn 60, will be a very different person from the paradigm in 1915, when the nation's estimated population passed 100 million, or even in 1967, when it topped 200 million.

The symbolic 300 millionth could be an immigrant, arriving by plane or crossing the border illegally, but most bets by those who study such things are on a native-born baby. About 11,000 are born each day.

"The 300 millionth will be a Mexican Latino in Los Angeles County, with parents who speak Spanish at home and with siblings who are bilingual," said William Frey, a demographer with the University of Michigan Population Studies Center.

"This is a far cry from the 200 millionth person who was born in the late 60's - probably a white son to middle-class suburbanites in Los Angeles or New York City," said Dr. Frey, rejecting Life magazine's determination, "and different from the 100 millionth person born in the late 1910's, perhaps to a white ethnic city family in New York City or rural family in upstate New York or Pennsylvania.

"The new baby is symbolic of America's new multi-ethnic demography of the 21st century, both urban and suburban, that will filter out from gateway cities like L.A., Dallas and New York, as white suburban boomers fade into the past," he said.

Carl Haub, a senior demographer for the Population Reference Bureau, a research group, concurred that the 300 millionth American is likely to be male - more boys are born than girls - and generally agreed with Dr. Frey about the baby's other characteristics, but left more wiggle room.

While most Americans are still Anglo-Saxon Protestants, Mr. Haub said, Hispanic mothers have higher birth rates, and no state has more births than California, where most newborns are of Hispanic origin. There, Jose ranked fourth in 2004 among the most popular baby names for boys after Daniel, Anthony and Andrew.

What is more certain is that the 300 millionth American will live longer - to 85 or 90 on average - and in a nation that will be more crowded.

Today, there are still plenty of wide-open spaces, with about 80 people per square mile in the nation. But density varies widely: some Texas counties are home to fewer than one person per square mile; Manhattan houses 67,000 per square mile.

"By the time the 300 millionth individual gets to adulthood, many of the cities today we consider small and nice to live in won't be so nice," Mr. Haub said.

The nation is also becoming more diverse and has been doing so much faster since the 1970 census than in the 50 years after the 1920 one registered the 100 millionth American.

"The baby who's born this year, as they grow up, they may not know what we mean by diversity," Mr. Haub said. "And somewhere along mid-century the word majority will disappear."

In 1915, experts differed about whether the 100 millionth was born in January or in April, but the 1920 census confirmed that the benchmark had been reached. In 1967, the Census Bureau acknowledged that, because of undercounting, the 200 millionth American had probably arrived two years earlier. Also, the official population clock was slowed slightly on the morning of Nov. 20, 1967, to accommodate President Lyndon B. Johnson's arrival at the Commerce Department for the ceremony.

That same year, David E. Lilienthal, the former chairman of the Atomic Energy Commission, warned in The New York Times that unbridled population growth might doom the nation to shortages of water and energy, bury it in pollution and saddle it with unmanageable poverty. "A population of at least 300 million by 2000 will, I now believe, threaten the very quality of life of individual Americans," he wrote.

Projections are subject to unimaginable imponderables - from the impact of wars and epidemics to dramatic gains in life expectancy. It has taken 230 years for the United States to reach 300 million people (the total number of people who have ever lived in America is obviously much higher). The Census Bureau projects that even with the nation growing more slowly than ever beginning in 2030, the population will top 400 million less than 40 years from now.

Does anyone really believe that the United States will be able to support a population of 400,000,000?