Supporters of SDLP Stormont minister, Margaret Ritchie, are predicting she will win the party leadership election by a two-to-one majority. However, campaigners for her rival, the party's deputy leader Dr Alasdair McDonnell, insist he will triumph by 30-40 votes.

A total of 420 SDLP delegates will chose their new leader at the party's annual conference next weekend. The result will be announced on Sunday. All SDLP elected representatives, members of the party executive, and representatives of local branches are eligible to vote.

Although Sinn Féin is failing to deliver on its promise of a united Ireland by 2016, the SDLP's poor performance has seen its vote deteriorate significantly. Ritchie, the North's social development minister, has the support of the majority of the SDLP assembly team including outgoing party leader Mark Durkan and policing spokesman Alex Attwood.

Other assembly members backing her are Declan O'Loan, Dolores Kelly, John Dallat, Conall McDevitt, Tommy Gallagher, Thomas Burns and Mary Bradley. However, McDonnell has the backing of some heavy hitters including SDLP deputy leader elect Patsy McGlone, assembly chief whip Pat Ramsey, and assembly group chairman Alban Maginness.

Other assembly members supporting McDonnell include Dominic Bradley and PJ Bradley. McDonnell is keen on the SDLP developing close links with Fianna Fáil, which Ritchie is understood to oppose.

The political styles of the two candidates couldn't be more different. McDonnell (60) is known for his direct, confrontational approach. The slogan, 'ABBA' – AnyBody But Alasdair – is used by his opponents.

McDonnell has been privately critical of Durkan's leadership and plans radical change if he wins. One of his campaign team says: "Margaret's trying to sell the vision thing. The problem is, the party already has rooms full of vision but we're unable to deliver it.

"Alasdair is about rebuilding organisation and finance. He's a successful businessman so he'll have no problem attracting funding. In terms of organisation, he'll kick ass. The days of paper party branches are over.

"He will also introduce a system of rigorous assessment for all elected representatives. If anybody doesn't perform, they'll be out." McDonnell will seek to rebuild relationships between party headquarters and hard-working, local councillors who feel they've been marginalised. Another supporter says: "Alasdair believes young people have been used in the past by the SDLP for window-dressing. He plans to build people's profiles continuously and particularly promote young women in the party."

McDonnell is predicting that without radical change, the SDLP will lose up to five assembly seats in next year's elections. One supporter says: "Alasdair appeals to the 'must do, will do' party member. Yes, he's a bull in a china shop but that's what the SDLP needs in order to survive, not further years of wishy-washiness. Alasdair alone has the gravitas and clout to take on the Shinners."

A McDonnell supporter describes Ritchie (51) as "Mark Durkan in a skirt – nice, well-meaning but ineffective". However, that is strongly challenged by her campaigners. "Margaret is more radical and decisive than Mark," one says.

"Margaret is the woman who stood up to the UDA when, as social development minister, she stopped funding for UDA-linked projects. She has proved she isn't frightened of anybody or anything."