Hispanics now account for more than half the U.S. population growth this decade, indicating a powerful new sign of their demographic clout, according to a Pew Hispanic Center report released Thursday.

The Hispanic population also expanded dramatically in the 1990s, but in that decade its growth accounted for less than 40 percent of the nation’s total population increase.

Hispanics now represent 50.5 percent of the U.S. population growth since 2000, although they were only 15 percent of the population in 2007.

The Pew report also highlights a significant new driver of the population increases for the nation’s largest minority: Unlike the 1990s when immigration was the major factor in Hispanic population growth, births in the U.S. are mostly responsible for the increases this decade.

Jeffery Passel, senior demographer at the Pew Hispanic Center, said Census data shows the Hispanic population has increased 10.2 million, from 35.3 million in 2000 to 45.5 million by July 2007.

A natural demographic increase — births minus deaths — is responsible for 6 million of the new Hispanic residents this decade. International migration — which among Hispanics has been calculated in the past to be two-thirds undocumented — accounts for 4.2 million of the increase, Passel said.

The Census Bureau’s figures do not distinguish whether immigrants are legal or illegal.