* Weyerhaeuser selling 140,000 acres of Oregon timberlands

* Sale to add $100 mln to third-quarter earnings

* In talks to sell another 82,000 acres in Washington

LOS ANGELES, Aug 13 (Reuters) - Weyerhaeuser Co (WY.N) said on Thursday it would sell 140,000 acres of Oregon timberlands for about $300 million and is in talks to sell additional lands in Washington state.

The sale, to an entity affiliated with timberland investment management firm The Campbell Group LLC, is expected to contribute about $100 million to Weyerhaeuser's third-quarter earnings, after taxes, it said in a statement.

"We have a competitive advantage in growing and processing Douglas fir, and the sale focuses our Western operations on managing that species," Weyerhaeuser Chief Executive Dan Fulton said in a statement. "While the land sold and for sale is high quality, productive timberlands, the stands are primarily hemlock, spruce and species other than Douglas fir."

The forest products company also said it is in talks to sell an additional 82,000 acres in southwestern Washington.

The land sold and for sale represents about 10 percent of the Federal Way, Washington-based company's holdings in the Pacific Northwest, it said.

Before Thursday's announcement, Weyerhaeuser shares rose 32 cents, or 0.9 percent, to close at $37.18 on the New York Stock Exchange.