Professor George Williams and Professor Greg Craven, Australia's leading federalism experts, agree the proposal is unlikely to get a majority of votes.

The warnings came as a senior Government source said it was feared South Australia's clout over Murray water would be weakened if the referendum failed.

The source said the Government expected upstream states - NSW, Victoria and Queensland - to vote for self-interest and reject a federal takeover.

"If the referendum were to fail, which is practically a dead cert, South Australia's interest over the Murray would go backwards," the source said.

Mr Abbott last week said that if elected the Coalition would hold the referendum in 2013 if significant progress to deal with water shortages in the river system had not been not made.

Professor Williams, who is the Anthony Mason Professor of Law at the University of NSW, said referendums that gave more power to the Federal Government were rarely successful.

''Thirty-six of 44 of referendums have been rejected in this country,'' Professor Williams said, ''and those which have sought more power for the federal government have been overwhelmingly rejected.''

The two most recent successful referendums that granted more power to the Commonwealth were in 1946 - granting the Commonwealth the right to hand out pensions and social security - and 1967, granting the right to make laws for indigenous people.

Professor Craven, the vice-chancellor of the Australian Catholic University, said the idea was ''not brilliant'' and likely to be rejected.

Referendums were normally on national issue and voters in Western Australian, and Tasmania would be uninterested at best, he said.

Professor Mike Young, the executive director of Adelaide University's Environment Institute, said it would take just one state government to run a scare campaign to ''scare the horses''.