WASHINGTON (AP)—The nation's population officially hit 300 million at 7:46 a.m. EDT Tuesday, when the Census Bureau's population clock rolled over to the big number.

But there weren't any wild celebrations, fireworks or any other government-sponsored hoopla to mark the milestone. Why bother? Many experts think the population actually hit 300 million months ago.

"I don't think anybody believes it will be the precise moment when the population hits 300 million,'' Howard Hogan, the Census Bureau's associate director for demographic programs, said in an interview before the milestone was reached. But, he added, "We're confident that we're somewhat close.''

It's not easy estimating the exact number of people in a country the size of the United States. It gets even more complicated when you take into account illegal immigration, another reason for the federal government to let the milestone pass quietly.

When the U.S. population officially hit 200 million in 1967, President Johnson held a news conference at the Commerce Department to hail America's past and to talk about the challenges ahead. Life magazine dispatched a cadre of photographers to find a baby born at the exact moment, anointing a boy born in Atlanta as the 200 millionth American.

This year, there's a good chance the 300 millionth American has already walked across the border from Mexico.

"It's a couple of weeks before an election when illegal immigration is a high-profile issue and they don't want to make a big deal out of it,'' said William Frey, a demographer at the Brookings Institution, a Washington think tank.

Commerce Secretary Carlos Gutierrez said the Bush administration isn't playing down the milestone, though he said he had no plans for Tuesday. Census Bureau employees planned to mark the moment Tuesday afternoon with cake and punch.

"I would hate to think that we are going to be low key about this,'' said Gutierrez, whose department oversees the Census Bureau. "I would hope that we make a big deal about it.''

Gutierrez said America's growing population is good for the economy. He noted that Japan and some European countries expect to lose population in the next few decades, raising concerns that there won't be enough young people entering the work force to support aging populations.

"This is one more area where we seem to have an advantage,'' Gutierrez said. "We should all feel good about reaching this milestone.''

The U.S. adds about 2.8 million people a year, for a growth rate of less than 1 percent. About 40 percent of the growth comes from immigration. The rest comes from births outnumbering deaths.

The Census Bureau counts the population every 10 years. In between, it uses administrative records and surveys to estimate monthly averages for births, deaths and net immigration. The bureau has a "population clock'' that estimates a birth every seven seconds, a death every 13 seconds and a new immigrant every 31 seconds. Add it together and you get one new American every 11 seconds.

The 300 millionth American—born months ago or on Tuesday—is probably Hispanic because they are the fastest growing demographic group in the U.S., Frey said.

Jeffrey Passel, a senior demographer at the Pew Hispanic Center, said the Census Bureau has improved its population estimates in the past few years, but it still undercounts illegal immigrants.

There are an estimated 11 million to 12 million illegal immigrants in the U.S. Experts differ on the specifics, but many estimate that more than 1 million of them don't show up in census figures.

"The census clearly misses people,'' said Passel, a former Census Bureau employee who used to help estimate the undercount. "Having said that, when they crossed 200 million, they were missing about 5 million people. We think the 2000 census missed a lot less than 5 million people.''

By Stephen Ohlemacher Associated Press