Plans to overhaul the House of Lords, shrinking it by a third and abolishing life peerages, have "a long way to go" to win cross-party support.
There have been years of deadlock on the future of the Lords
Leaked proposals from Commons leader Jack Straw suggest the Lords could be half elected, and half appointed.
But the Lib Dems and Tories said the Lords needed to be largely, if not wholly, elected.
MPs and peers have failed to agree on reform since 1999 when 600 hereditaries lost their seats.
Mr Straw chairs a cross-party committee which is trying to get a consensus on the future of Parliament's second chamber.
But reaction to his proposals, leaked to the Sunday Times, suggest there is still some way to go.
Lib Dem constitutional affairs spokesman Simon Hughes said the proposals were a "welcome first stab" at reform and a "certain amount of common ground" was developing.
"But Jack Straw has so far failed to grasp the fundamental point: the replacement of the House of Lords must be predominantly elected," he added.
Conservative Leader in the House of Lords, Lord Strathclyde, said there was a "long way to go".
"We are in favour of replacing Labour's cronyism with an elected House of Lords with more powers which will be better able to hold an over-mighty government to account," he said.
And Tory MP Sir Patrick McCormack criticised any plan to create "another class of professional politician which would be inordinately expensive".
The newspaper reported that the proposals include quotas for women and ethnic minorities, and a salary for Lords, who would be expected to work full time.
The proposals are Mr Straw's attempt to "facilitate discussion"
The upper chamber would shrink further from 741 members to 450 - with no single party able to command an overall majority.
A commission of nine members, three selected by the party leaders, would make appointments.
The Campaign for a Democratic Upper House also urged that the reforms go further.
Co-ordinator Damien Welfare, co-ordinator said it sounded like a major step forward but added: "A majority of the members need to be directly elected to achieve a true democratic reform."
A White Paper is due to be produced towards the end of October, leading to a free vote in both Houses of Parliament before Christmas.
A government spokesman said the document was not government policy, but an "attempt to facilitate cross-party discussion".
After 1999, the number of hereditary peers was reduced to 92, and further changes were expected in Labour's second term.
But plans were shelved because MPs could not agree which of seven options to take - from an all-appointed upper house to a fully-elected one.