Advocates for more pro-growth policies in New York will get new ammunition today with the release of a report from the U.S. Census Bureau showing that the Empire State was one of only a handful of states that lost population this year, with thousands of people moving away to other parts of America and not being replaced by new residents.

The state lost more than 9,500 people between July 2005 and July 2006, putting its total statewide population at 19.3 million, according to the federal statistics. Only states like Michigan, which has been hard-hit by the decline in the domestic auto industry, and hurricane-ravaged Louisiana, which lost 4.9% of its population due to the storm, saw a more dramatic decline, the bureau estimated.

Just weeks before today’s statistical estimates, which aren’t based on an actual enumeration or head count, Mayor Bloomberg predicted that the city would gain about 1 million people by 2030.

Still, the Census Bureau’s stagnant prediction about New York State came days after the Bloomberg administration released statistics showing that the birth rate in New York City hit a 25-year low in 2005. The actual number of births in the city was 122,725, or 1,374 fewer than in 2004.

The specter of young people fleeing New York State, especially upstate, because of a lack of jobs was a central theme in this year’s gubernatorial campaign, with governor-elect Spitzer likening parts of upstate to Appalachia in terms of economic desperation.

A professor of urban policy and planning at the Wagner School of Public Service at New York University, Mitchell Moss, said the population news is part of a “continuous cycle of decline” in parts of New York for a generation.

“Smart, young, ambitious, and creative people have been forced to leave Upstate New York because of a lack of opportunities,” Mr. Moss said.

A senior fellow who directs the Manhattan Institute’s Empire Center for New York State Policy, E.J. McMahon, said yesterday that upstate economy could comfortably accommodate a “huge population” compared to how many people live there, but changes to government policies are needed to “unshackle” the region and put spur economic development.

For New York City, immigrants fill some of the void left by ex-New Yorkers. Mr. McMahon suggested that zoning restrictions and taxes hinder job creation.

“New York State’s leading export is people,” Mr. McMahon said, “however, New York State’s leading import is also people.”

Robert Ward of the Business Council of New York State told the Associated Press that the population loss can be partly attributed to people heading to Texas and other states that are growing jobs at a faster rate.

“People are moving elsewhere in search of opportunities that they’re not finding in New York,” Mr. Ward told the AP.

A demographer who represents New York State to the Census Bureau on population estimates, Warren Brown of Cornell University, predicts that several of the larger counties will mount official challenges to the data once estimates broken down by county are released early next year.

“I think the estimates are wrong,” Mr. Brown said. “They’ve been wrong the past few years.”

Immigrants, college students, and people with lower-incomes can be particularly difficult to count accurately, he said, and many are often missed when the Census Bureau releases its estimates each year.

To challenge the Census Bureau’s numbers, local demographers show their federal counterparts locally available housing data, such as building permits and certificates of occupancy.

“It’s not fair to the states to portray them having a lower population than they do,” Mr. Brown said.

A census spokesman said a bureau demographer wasn’t immediately available last night to comment on the dispute over the study’s methodology.

The Census Bureau’s estimates for seven counties in 2005 — including New York City, Rockland, and Westchester — lowballed the Empire State’s population by a total of almost 80,000 people, Mr. Brown said. After the statistics were revised, he said, the totals actually reflected a modest population growth of 24,000.

Mr. Brown says the revisions tend not to attract as much public attention as the original findings.

Among the census bureau’s other findings were that between 2005 and 2006, California was the most populous state, with 36.5 million; Texas has gained about 579,000 people, the most of any state, and Arizona’s population, which rose 3.6%, grew faster than any other state.