Nick Clegg's campaign to become Lib Dem leader appears to be gathering pace, with senior figures offering support.
Mr Clegg has yet to make an announcement that he will run
Steve Webb, the party's manifesto writer, said he was backing Mr Clegg - the home affairs spokesman - and would take "several" other MPs with him.
Former leader Lord Ashdown and finance spokeswoman Julia Goldsworthy have also pledged their support.
Mr Webb ruled out running on Thursday, with Environment spokesman Chris Huhne the only declared contender so far.
Mr Webb - seen as being on the left of the party, unlike Mr Clegg and Mr Huhne - had been widely expected to run, and his decision increases the prospect of a two-horse race.
In a statement, Mr Webb said he had had enough support among MPs to stand and had seriously considered entering the race.
But the "huge cost" to his family and Mr Clegg's abilities had persuaded him against it.
Mr Webb said: "I have been overwhelmed by the many messages of support and encouragement that I have received since first indicating that I would consider running as leader of the party."
He added: "I have seriously considered standing, but have now made the positive choice to step aside and to give my support to Nick Clegg.
DECLARED CLEGG BACKERS
"I believe that my work with colleagues on our policy platform has given us a firm foundation as a party.
"We now need a leader who will excel in communicating those core Lib Dem values and policies and who has the strategic political judgment that we need.
"I believe that Nick best combines those qualities and can take our party on to a new level. "
Mr Clegg, MP for Sheffield Hallam, welcomed Mr Webb's backing and declared the support of Lord Ashdown and Ms Goldsworthy.
He said: "Steve is a very innovative policy thinker and a powerful figure in the party. I am delighted to have his endorsement.
DECLARED HUHNE BACKERS
"He shows that I want to bring the party together to make a powerful and distinctive appeal to the country."
Mr Clegg is expected officially to launch his campaign on Friday.
Acting leader Vince Cable, transport spokeswoman Susan Kramer and elections co-ordinator Ed Davey have all ruled themselves out of the race.
Former Lib Dem leader Charles Kennedy said it was "highly unlikely" he would stand again, adding: "You should never say never in politics, but as close to never as you can get."
Birmingham Yardley MP John Hemming is still hoping to gain the necessary seven MPs' support so he can enter the race.
But he has admitted on his weblog that "there is going to be a challenge getting nominated".
The leadership race was sparked by the resignation of Sir Menzies Campbell, who blamed the media's obsession with his age.
At his campaign launch, Mr Huhne, who was defeated by Sir Menzies in the 2006 leadership contest, said he wanted the party to be committed to the idea that "everybody's individual worth and chance is given its full possibility".
The green agenda, for which he is known, would play "a big part in the campaign", he added.