The Atlanta Journal-Constitution will reduce its circulation area to 27 counties in and around metro Atlanta and cut 56 full-time and 100 part-time jobs as the media industry faces “unprecedented economic challenges,” the company said Wednesday.

The cutback — the third such move since early 2007 — will eliminate circulation to 22 counties: Banks, Butts, Dawson, Fannin, Gilmer, Greene, Habersham, Haralson, Heard, Jackson, Lumpkin, Morgan, Pickens, Rabun, Spalding, Towns, Troup, Union, and White in Georgia, along with Cherokee, Clay and Macon counties in North Carolina. The change is effective Jan. 11.

The move will reduce daily and Sunday circulation about 5 percent. But it will not significantly affect overall readership — a measure of readers rather than the number of copies — because that is based on a 28-county area, the AJC said.

The company said 215 employees have been offered involuntary severance packages as part of a restructuring of the circulation department, but that they may apply for 59 jobs created by the changes. The net reduction is 156 full- and part-time positions.

Metro newspapers around the country are grappling with revenue declines that have worsened amid the economic downturn this fall. Expanded online operations have so far not generated enough revenue to offset the drops.