Washington ? About one in every 37 U.S. adults was either imprisoned at the end of 2001 or had been incarcerated at one time, the government reported Sunday.

The 5.6 million people with “prison experience” represented about 2.7 percent of the adult population of 210 million as of Dec. 31, 2001, the report found. The study by the Justice Department’s Bureau of Justice Statistics looks at people who served a sentence for a crime in state or federal prison, not those temporarily held in jail.

The study is the first to measure the prevalence of prison time among American adults. Last month, the bureau reported that a record 2.1 million people were in federal, state or local custody at the end of 2002.

Between 1974 and 2001, the number of current and former inmates rose by 3.8 million, the study found. Of those, 2.7 million were former inmates.

Experts say the growing numbers of ex-prisoners means more people in society have difficulty finding jobs because they have felony convictions. Many cannot vote and they are more likely to have family or emotional problems that exact a toll on state and local government budgets.

“We’re talking about a large number of people — bigger than a lot of countries in Western Europe — who face the barriers that exist when you have been in the correctional system,” said Jason Zeidenberg, director of policy and research at the Justice Policy Institute, which advocates alternatives to prison. “That’s a really upsetting number.”

The number of people sent to prison for the first time tripled from 1974 to 2001 as sentences got tougher, especially for drug offenses. There are more ex-prisoners as well, the result of longer life expectancies and a larger U.S. population.

Prison experiences vary greatly by gender and ethnic origin.

“At every age, men have higher chances of going to prison than women, and blacks and Hispanics have higher chances than whites,” statistician Thomas P. Bonczar said in the report.

Almost 5 percent of men in 2001 had done prison time, compared with less than 1 percent of women.

Almost 17 percent of black men in 2001 had prison experience, compared with 7.7 percent of Hispanic men and 2.6 percent of white men. The percentage of black women with prison time was 1.7 percent, compared with less than 1 percent of Hispanic and white women.

No matter their ethnic origin, people between ages 35 and 44 in 2001 had the highest rates of lifetime incarceration — 6.5 percent for men, almost 1 percent for women.

About one-third of the former prisoners in 2001 still were under correctional system supervision, including 166,000 in local jails. The rest were either on parole or on probation.

The study projects that, by 2010, about 3.4 percent of the adult U.S. population will have had served time in prison. That translates to about 7.7 million people.

If 2001 incarceration rates remain the same, about 6.6 percent of people born that year can expect to serve a prison sentence during their lifetimes, based on life expectancy tables, the study said.

That compares with 5.2 percent of those born in 1991 and 1.9 percent of people born in 1974, according to the estimates.

About 11.3 percent of men and 1.8 percent of women born in 2001 will go to prison during their lifetimes. For black males, that translates into a one in three chance of doing time, compared with one in six for Hispanic males and one in 17 for white males, according to the projections.