SYDNEY (Reuters) - Australia's Fairfax Media on Wednesday rejected calls from mining magnate and top shareholder Gina Rinehart for board representation, saying it would not compromise its editorial independence.

Rinehart, the Asia-Pacific region's richest woman with a fortune estimated by Forbes at $18 billion, has built an 18.7 percent stake in the publisher of the Australian Financial Review and Sydney Morning Herald. Rinehart had been seeking up to three seats on the board.

"I regret that agreement has not been reached for Mrs Rinehart to join the Fairfax Media board of directors," Fairfax Chairman Roger Corbett said in a statement.

"I hope that this might be possible in the future. However key elements yet to be agreed include acceptance of the charter of editorial independence as it stands and the Fairfax board governance principles as agreed by all existing directors."

Rinehart, a critic of Australia's Labor government and its controversial mining and carbon taxes, has pitched herself as a white knight for Fairfax. But said she might sell her stake in the media company, which is struggling with a fragmented advertising market and shift in the publishing landscape, if she did not get influence at the board level.

"Unless director positions are offered without unsuitable conditions, Mrs Rinehart is unable to assist Fairfax at this time," Rinehart's company, Hancock Prospecting, said in an email statement to the Australian Broadcasting Corp that was published on Tuesday.

Rinehart also owns 10 percent of TV broadcaster Ten Network and has a seat on its board. Hancock did not immediately respond to a request for comment.

Shares in Fairfax closed on Wednesday up 0.9 percent at A$0.555, just off an all-time low of A$0.53 touched on Tuesday. The stock peaked near A$5.00 in 2007.

(Reporting by Lincoln Feast; Editing by Chris Gallagher)