Alexandria officials last night unveiled a plan to build a $19 million "public safety center" designed to replace the dilapidated city jail in Old Town, part of which is 158 years old, and consolidate the offices of the police department, sheriff and magistrates.

The facility, scheduled for completion by late 1985, will be located near the Eisenhower Avenue Metro Station near the Capital Beltway.

Last night the city's Planning Commission unanimously approved the center's preliminary plan, which calls for a shopping mall-like complex anchored on its east side by the six-level jail structure, on a wooded nine-acre industrial site.

"I happen to believe that this facility is needed to allow us to constitutionally serve those persons who are incarcerated here," said Alexandria Sheriff Michael E. Norris, who is in charge of the jail.

The city is under a federal court order, resulting from an inmates' suit, to improve jail conditions and replace the existing facility, which is at 517 Princess St., by 1986. The inmates argued that conditions at the jail--particularly regarding health and fire safety--constitute "cruel and unusual punishment."

City officials said the new center will employ the latest available technology: computer-controlled heating, venting and air-conditioning; electronic records storage, and possibly robots to shuttle mail and perhaps monitor inmates asleep in their cells. Instead of bars, windows will be glazed with supposedly unbreakable glass. There will be an assortment of classrooms, a chapel, medical treatment unit, indoor and outdoor recreation areas, separate cells for juveniles and specially designed cells for handicapped inmates.

"We're demanding the latest state-of-the-art equipment," Norris said. "We are going to have to live with the facility for the next 50 to 100 years."

The new jail will have more than twice the floor space of the existing one and make more efficient use of that space, almost tripling the current jail's 98 inmate capacity, according to Capt. Eric Geiger, project director for the sheriff's department.

The existing jail and 24-year-old police headquarters building behind it are expected to be demolished, city officials said. The planning commission recently rezoned the property for residential development.