By Vanessa Allen writing in The Daily Mail.
Publishing sources say they could be paid up to £1million.
The couple's spokesman, Clarence Mitchell, stressed they wanted to raise money for the dwindling Find Madeleine appeal and to counter a campaign of smears by Portuguese police.
Last week it emerged that the former head of the Madeleine investigation, Goncalo Amaral, has written a book about the case with the working title The Truth of the Lie.
Insiders said it will contain 'explosive' details about the police inquiry and the decision to name the McCanns as official suspects, or arguidos.
Mr Mitchell confirmed that Mr McCann, 39, had talked to one publishing house and been approached by several others.