ALBANY — Most of upstate New York continues to lag behind downstate and the rest of the country in population growth. If current trends continue, upstate could cede even more political power in Albany to downstate districts, while the state as a whole could lose federal representation.

In a press conference Wednesday, the New York State Association of Counties presented county population estimates from the U.S. Census Bureau for the period of April 1, 2000, through July 1, 2007. Culled from examinations of local birth and death rates, as well as migration within the state, and international migration, these estimates paint a bleak picture for much of upstate.

"Of the 33 counties that lost population since the last census, 32 are upstate," said Jeffrey Osinski, NYSAC's director of research and education. He added that only three of New York's counties grew at a rate exceeding the national population growth rate of 7.2 percent.

As a whole, New York had a population growth rate of 1.7 percent, ranking the state 43rd in the nation, he said. Five counties, all of which are upstate, grew less than 1.7 percent since 2000, Mr. Osinski said. Thus, 38 counties either lost population or grew at less than the state's overall 1.7 percent rate.

"State and county leaders are concerned about our flat growth," said Stephen J. Acquario, NYSAC's executive director. "The fact that 38 of our counties either lost population or have grown at less than the state rate ... is a troubling trend. If it continues, we will have fewer taxpayers to pay for an increasing number of services at a time when our property taxes are already too high."

During the same period, Florida's population grew by 14.2 percent. That state now has about 1 million fewer residents than New York, Mr. Osinski said.

In the north country, Essex, Franklin, Lewis and St. Lawrence counties lost population between 2000 and 2007. Only Jefferson and Clinton counties grew at rates greater than the state's anemic 1.7 percent. In Jefferson, with a 3.7 percent growth rate, the increase may be attributed to the large military presence at Fort Drum. Clinton's growth is likely due to a concentration of high-tech industries at the former Plattsburgh Air Force Base and the county's proximity to Montreal.

Net migration measures movement of people into or out of a region. New York had a net migration rate of negative 2 percent. In the north country, Franklin, Lewis and St. Lawrence counties experienced greater negative net migration than the state rate, while Essex and Jefferson counties had negative net migration that was less that the state's negative 2 percent. Only Clinton County had positive net migration between 2000 and 2007.

If these trends continue, the potential effects on the Empire State as a whole and on upstate in particular could be dramatic.

■ New York could lose at least two seats in the House of Representatives after the 2010 federal census.

■ Four upstate Congressional districts, the 25th, 26th, 27th and 28th, all in Western New York, are located almost entirely in areas of population loss.

■ Districts in the state Assembly will shift from areas of population loss (upstate) to areas of population growth (Hudson Valley, New York City and Long Island).

■ New York will continue to lose federal funding that is based on population.

Warren A. Brown, director of the applied demographics program at Cornell University, Ithaca, said that municipal and local officials should review the population estimates for their respective jurisdictions and not hesitate to challenge estimates they believe to be low. He said that Jefferson County challenged three recent estimates, in 2002, 2004 and 2006, resulting in the addition of a total of 11,631 residents.

Mr. Brown added that in only one case has such a challenge resulted in a lower population estimate, which was a unique situation on which he did not elaborate.

Robert Scardamalia, director of the New York Data Center at Empire State Development, said the state's population will continue to age, mirroring a national trend. He noted that approximately one-third of people leaving upstate relocate to areas around New York City.