The chief spokesman, Joaquin Navarro-Valls said: 'The Holy See is conscious that what is under discussion is the future of humanity.' He went on to outline the Vatican delegation's position for the 5-13 September conference.
'If a consensus is reached in Cairo, which will be what almost everyone is expecting, certain positions have to change regarding the consideration of abortion as a means of family planning,' Mr Navarro-Valls said.
'The other possibility is to approve the (final) document without consensus, without unanimity. Nobody will be pleased with that.'
Asked whether Pope John Paul held the key to the success or failure of the conference at which the Vatican has a vote, Mr Navarro-Valls said: 'You can put it that way. I prefer to say that good sense should prevail in Cairo.'
Pope John Paul has spearheaded a Vatican campaign to influence the outcome of the meeting, which he fears will sanction abortion.
In his latest assault on language in a draft document prepared for the gathering, the Pope told pilgrims on Sunday that the Vatican wanted the final conference statement explicitly to exclude abortion as a means of birth control.
The Cairo conference aims to draw up a 20-year plan to stabilise world population by quadrupling money given to poor nations for family planning, health care and primary education for girls.