ATLANTA (AP) _ Georgia-Pacific Corp. on Thursday reported net income of $67 million or 61 cents per share for the second quarter of 1985, down from $84 million or 78 cents per share in the same quarter last year.

T. Marshall Hahn Jr., chairman and chief executive officer of the Atlanta- based forest products company, said depressed conditions in the paper market were offset during the quarter by the strong showing of Georgia- Pacific's building products business.

The operating profits of the building products division rose from $98 million last year to $122 million in the second quarter of 1985, while the operating profits of the pulp and paper segment dropped from $56 million to $11 million in the same period, Hahn said.

''Pulp and linerboard have been particularly affected by the strong U.S. dollar, with conditions in export markets causing inventories to accumulate in the United States (and) resulting in prices substantially below year-ago levels,'' he said.

For the six months ended June 30, Georgia-Pacific reported net income of $116 million or $1.04 per share, down from $135 million or $1.23 per share in the first half of 1984.

The company said sales totaled $1.79 billion in the second quarter of 1985, up from $1.67 billion a year ago, and sales for the first half of this year were $3.37 billion, up from $3.16 billion.