Stoiber is the right's preferred candidate

Ms Merkel, leader of the Christian Democratic Union, is seen as a lacklustre figure.

Mr Stoiber, leader of the Christian Social Union, is more experienced, and further to the right.

The BBC's correspondent Rob Broomby says Mr Stoiber victory guarantees a more colourful - although perhaps more divisive - campaign.

His party has repeatedly refused government appeals to keep inflammatory issues like immigration out of the election.

Although polls put Mr Stoiber ahead of Ms Merkel, they also suggest that Mr Schroeder remains in the lead overall.

Stoiber favoured

According to the latest poll, published by the Tagesspiegel newspaper on Friday, Mr Schroeder would win 58% of the vote if the position were directly elected, against 39% for Mr Stoiber, and 32% for Ms Merkel.

Among supporters of the centre-right parties, there was a clear preference for Mr Stoiber as candidate for the chancellorship, by 76% to 60%.

Earlier this week, Mr Stoiber, who leads the Christian Social Union, said the two hopefuls would reach an amicable agreement on who would stand.

Otherwise, he indicated, the issue could be decided by MPs in the Bundestag.

Correspondents say MPs are not confident of victory under Mr Stoiber, but that most see him as the best chance they have of holding on to their seats.