* Talk of high-profile resignation rocks Japan politics
* Inada at center of scandal related to peacekeeping mission
* Turmoil erodes support for Japan PM Abe (Recasts story)
TOKYO, July 27 (Reuters) - Japan's embattled Defence Minister Tomomi Inada will resign on Friday over the suspected cover-up of information related to a U.N. peacekeeping mission and a former defense minister is already lined up to take her place, media said.
A spokeswoman at Inada's office on Thursday declined to comment on whether she would resign, which was first reported by broadcaster NHK.
Inada had launched an investigation into media reports that defense officials had tried to hide logs showing worsening security in South Sudan, where Japanese troops were taking part in a U.N.-led peacekeeping operation.
Inada will resign after Friday's publication of the results of the investigation to take responsibility for the affair, according to NHK.
Inada, a protege of Prime Minister Shinzo Abe, had denied reports of involvement in the cover-up but had been expected to be replaced in a cabinet reshuffle likely early next month because of the scandal, and a series of missteps that critics say contributed to a plunge in support for Abe.
Kyodo news agency said Abe was likely to choose as her successor somebody who had already served in the post, trying to project an image of stability as he battles a number of scandals.
Potential candidates include Itsunori Onodera, Kyodo said, who served as defense minister for nearly two years from 2012, when Abe returned to power, and is widely regarded as a safe pair of hands for the job.
The cover-up scandal has also led General Toshiya Okabe, chief of staff of the Ground Self Defence Forces, to decide to resign, media reported. A defense ministry spokesman declined to comment. (Reporting by Elaine Lies; Editing by Paul Tait and Clarence Fernandez)