A co-author of a Bureau of Justice Statistics report, Paige Harrison, linked an upswing in the rate of arrest for women to their increased participation in drug crimes, violent crimes and fraud.

The number of women incarcerated in state and federal prisons in 2004 was up 4 percent compared with 2003, more than double the 1.8 percent increase among men, the study said. In 1995, women made up 6.1 percent of all inmates in those facilities.

"The number of incarcerated women has been growing ... due in large part to sentencing policies in the war in drugs," The Sentencing Project, a group promoting alternatives to prison, said in a statement.

The group said the number of drug offenders in prisons and jails has risen from 40,000 in 1980 to more than 450,000 today. According to FBI figures, law officers in 2004 made more arrests for drug violations than for any other offense — about 1.7 million arrests, or 12.5 percent of all arrests.

Those sentenced for drug offenses made up 55 percent of federal inmates in 2003, the report said.

The total number of people incarcerated grew 1.9 percent in 2004 to 2,267,787 people. That figure includes federal and state prisoners, as well as 713,990 inmates held in local jails, 15,757 prisoners in U.S. territorial prisons, 9,788 in immigration and customs facilities, 2,177 in military facilities, 1,826 in Indian Country jails and 102,338 in juvenile facilities.

The country's state and federal prison population — 1,421,911, which excludes state and federal prisoners in local jails — grew 2.6 percent in 2004, compared with an average growth of 3.4 percent a year since 1995.

Growth last year in federal prison populations was 5.5 percent, outpacing overall prisoner growth but slipping from the 7.4 average annual growth in federal prison populations since 1995. The number of inmates in state prisons rose 1.8 percent, with about half that growth in Georgia, Florida and California.

Harrison attributed some of the prison population rise to tougher sentencing policies implemented in the late 1990s. She said the average time served by prisoners today is seven months longer than it was in 1995.

"You bring more people in, you keep them longer — inevitably you're going to have growth," she said.

The Sentencing Project said the continued rise in prisoners despite falling crime rates raises questions about the country's imprisonment system. The group said the incarceration rate — 724 per 100,000 — is 25 percent higher than that of any other nation.

"Policy-makers would be wise to reconsider the wisdom of current sentencing and drug policies, both to avoid expensive incarceration costs and to invest in more productive prevention and treatment approaches to crime," Marc Mauer, the group's executive director, said in a statement.

Another group, The Justice Policy Institute in Washington, said the statistics show little relationship between prison population growth and the crime rate, which has been falling in recent years.

"The nation does not have to lock more people up to have safer communities," said Jason Ziedenberg, the institute's executive director.

About 8.4 percent of the country's black males between the ages of 25 and 29 were in state or federal prison, compared with 2.5 percent of Hispanic males and 1.2 percent of white males in the same age group, the report said.

Blacks made up an estimated 41 percent of inmates with a sentence of more than one year, the report said.