The Liberal Democrats were too "inward looking" under the leadership of Sir Menzies Campbell, party leader hopeful Nick Clegg has said.
Mr Clegg is the bookie's favourite to win the contest
Mr Clegg, the front-runner in the leadership contest, said he wanted to end the "mould of two-party politics".
Meanwhile, his rival Chris Huhne has reportedly said he would scrap the Trident nuclear weapons system.
But Mr Clegg said he was not prepared to unilaterally disarm "on a whim in a leadership contest".
Mr Clegg, the party's home affairs spokesman, told ITV1's Sunday Edition: "What I seek to do is draw a line under two years of what has been, frankly, a rather introverted, somewhat inward-looking phase in the party's history."
He pledged to set an ambitious objective to "break the stifling mould of two-party politics within the next decade".
In Sunday's Observer newspaper Mr Huhne - the party's environment spokesman - said it would be "ridiculous" to replace the existing Trident system with "something of equivalent power, strength and lack of vulnerability".
His stance signalled a break with the party's policy on Trident which has been to delay making a decision on replacing the submarines.
Mr Clegg said his rival was not committed to "scrap Trident tomorrow".
He added: "I start with two principles. I'm a nuclear disarmer but I am, to my fingertips, a multi-lateralist.
"I do not believe that, just on a whim in a leadership contest, one should abandon the idea that Britain should play a role not only in disarming itself but disarming the world."
Mr Clegg is the bookies' favourite and frontrunner at Westminster after submitting nomination papers signed by 28 of the Lib Dem's 63 MPs - almost triple the 10 nominations secured by his rival.
The contest will be decided by a ballot of the party's entire membership, but the figures suggest a strong preference for Mr Clegg among the MPs the winner will lead at Westminster.
Ballots will be sent out in mid-November to members and the victor announced in mid-December.