PORTLAND – While the number of Maine’s residents older than 65 has increased slightly in the last three years, the number of residents younger than 13 in Maine has plunged, according to census estimates released Wednesday.

Between 2000 and 2003, the number of children ages 5 to 13 dropped 7.5 percent, far below the 0.7 percent decline nationally, according to the Census Bureau. Only four states – Vermont, North Dakota, Montana and Wyoming – had steeper declines.

The number of Maine children under 5 fell nearly 5 percent, while the same age group increased by 3 percent nationally, the figures show. Only Connecticut, North Dakota and Vermont fell more sharply.

The decline in the state’s under-13 population is the result of several variables, most notably a perceived reduction in the birth rate, said Joyce Benson, an economist with the State Planning Office.

“If you look at the age of the population, the baby boomer age group is basically pushing into their 50s,” Benson said. “So the portion of people that are in their child-bearing age is smaller than it was 10 or 15 years ago.”

Conversely, the number of Mainers 18-24 increased 16.2 percent from 2000 to 2003, the second-steepest increase of any state. Alaska had a 21.4 percent increase.

The number of Mainers 65 and over grew 2.7 percent, while those 85 and over increased 8.5 percent.

Benson cautioned that the numbers were preliminary estimates and will likely change with further examination. The Census Bureau released overall state estimates for 2003 last fall. The latest release offers a more detailed breakdown by age groups.

Nationally, the U.S. population has risen 3 percent since 2000 to nearly 291 million. In Maine, the population now stands at 1.3 million, up 2.4 percent from 2000, according to the census figures.