The inmate population at the crowded Calvert County Detention Center will more than double over the next 20 years, a study released this week projects.

The facility, which was designed to hold 132 prisoners, houses an average of 212 inmates a day, according to the report, which was completed by the consulting firm Carter Goble Lee for the Board of County Commissioners.

By 2025, the center will need to house 425 prisoners, the study found. The report said the county's facility would need 469 beds to accommodate daily fluctuations of the inmate population.

"We're going to have to do something to expand the detention center," said Sherrod Sturrock, the county's capital projects coordinator. "We need to start moving forward on this."

The commissioners voted last summer to expand the detention center. In doing so, they decided to spend up to $10,670 on a consultant to determine the scope of the jail project.

County officials said it is too early to put a price tag on the expansion project, but commissioners President David F. Hale (R-Owings) said the estimated cost would run from $10 million to $20 million.

Bruce Orenstein, a senior associate with Carter Goble Lee, said the state would cover all the capital costs if the county agreed to house inmates from the state prison system for the last 18 months of their sentence.

The study found that the county is housing many of those inmates. Orenstein said Calvert County judges preferred sentencing inmates back to the county's detention center because they distrusted operations at state-run jails.

"They had a lot more confidence in the local correction incarceration facility," he said.

The study said the facility, even accounting for acceptable double bunking of inmates, should have a rated capacity of 172 prisoners. Robert W. Lusby, the detention center's administrator, said the center assigns three prisoners to a cell in some cases to fit all 212 inmates into the facility.

The study found a number of reasons for the increase in prison population. Although the number of arrests and reported crimes declined slightly from 1998 to 2002, violent crime rose at an annual rate of 12.4 percent over the same period of time.

The implementation of a central booking process last year also contributed to a big increase in the admission of prisoners. All prisoners are processed at the detention center, off Route 231 just west of Prince Frederick, rather than by sheriff's officers off-site. That change caused annual admissions to the detention center to rise from 1,543 inmates last year to a projected 2,946 inmates this year.

The county commissioners expressed concern about the crowding and said they would discuss the report with judges and the state's attorney before deciding how to proceed.

Sturrock said the commissioners will need to make decisions soon about the prison expansion.

"At some point," she told the commissioners Tuesday, "we are going to need clear direction on how you want us to proceed."