Mr Kennedy, front-runner in a crowded race with seven potential candidates, has distanced himself in the past from Mr Ashdown's policy of working closely with Tony Blair.
Although many Liberal Democrat activists are critical of Mr Ashdown's strategy, Mr Kennedy has decided not to "play to the gallery" in the election by promising to weaken links with Labour. He will say that the cabinet committee on which senior Liberal Democrats sit alongside Labour ministers will continue its work if he becomes leader, although he will not extend its remit.
"The committee has been a success and he would continue with it," said one close ally. At the same time, Mr Kennedy will promise to ensure the Liberal Democrats maintain their distinctive identity and are not swallowed up by Labour.
However, the offer of co- operation will not extend only to Labour. Yesterday Mr Kennedy told BBC News Online that he would extend the co- operation to pro-European Tories such as Kenneth Clarke.
Today Mr Kennedy will throw his hat into the ring when he speaks to his local party in Ross, Skye and Inverness West. "Everyone acknowledges that Charles is a brilliant communicator," said his campaign manager, Matthew Taylor, MP for Truro. "He is also well placed to keep the party united, since he is a team player and his views reflect the centre of gravity in the party."
The two other candidates out of the blocks today will be Jackie Ballard, MP for Taunton and the party's women's issues spokeswoman, and David Rendel, MP for Newbury and social security spokesman.
Ms Ballard will outline an unashamedly left-of-centre manifesto and will concentrate on tackling poverty and social issues.
The third main opponent of Lib-Lab co-operation is Simon Hughes, MP for Southwark North and Bermondsey and health spokesman. Mr Hughes, one of the best-known and longest-serving of the party's MPs, was the first to declare his candidacy when the European polls closed at 10pm last night.
Don Foster, MP for Bath and Liberal Democrat education spokesman, will unveil his campaign on Tuesday. Malcolm Bruce, the party's Treasury spokesman, will announce today that he will be a candidate, and Paul Tyler, the party's chief whip, has said he may enter the race before the ballot starts at the end of this month.
The extent of Mr Ashdown's closeness with Mr Blair was highlighted last night when it emerged that as recently as last summer he offered to take his party into a coalition with Labour. Under the deal, rejected by Mr Blair, the Liberal Democrats would have had seats in a cabinet after the next election if Mr Blair promised to campaign for proportional representation.