U.S. population growth is slowing, according to the latest estimates from the Census Bureau, even as the Hispanic population swells.

Figures released Monday suggest the nation's population is between 305.7 million and 312.8 million.

The middle estimate of 308.5 million would be an 8.8 percent increase since 2000, down substantially over the previous decade's 13.2 percent growth.

Even the highest estimate would mean the population grew by only 11 percent.

Census Bureau officials said most of the uncertainty is linked to the difficulty of estimating how many people have immigrated to the United States, legally and illegally.

The new figures also confirm earlier research showing huge growth in the number of young Hispanics.

"That's absolutely dramatic demographic change," said Luis Salinas, a sociologist at the University of Houston, who noted that the growth is highest for children 3 and younger, as birth rates in the white, black and Asian populations dropped during the recession.

Hispanic birth rates dropped, too, but not as much, he said.

The figures released Monday aren't the official 2010 Census count but were based on birth and death records, Medicare enrollments and estimates of international migration.

They are intended to represent the total population on April 1, broken down by age, gender and race.

The initial results from the 2010 Census, including state population figures, will be released later this month. That will be used to determine how congressional seats will be apportioned.

Texas is expected to gain three or four additional seats.

Census director Robert Groves said the data released Monday won't be used to make corrections or other changes to the official census count.

But he said it is still important, partly because comparing actual census data with the estimates will help demographers determine how to make future counts more accurate.

"All of these things are flawed in different ways … but they're all useful," he said.

Jason Devine, chief of the bureau's methodology, research and development division, said the new figures present a snapshot of the nation on April 1 rather than an analysis of change over the past decade.

Still, some conclusions seem clear.

The figures show that Hispanics are growing as a percentage of young people. They now represent as much as 25 percent of people younger than 20, up from 17 percent in 2000.

Salinas said the figures will be even higher in the Southwest as Hispanic birth rates overtake relatively low birth rates for other groups.

The first set of data from the 2010 Census is required by law to be released by Dec. 31. Groves wouldn't give a date but said the bureau will meet the deadline.

jeannie.kever@chron.com