By Thomas Escritt and Jesús Aguado AMSTERDAM/SANTANDER, Spain (Reuters) - The two politicians vying to chair the council of euro zone finance ministers, a key role in the Greek debt crisis, set out their stalls on Tuesday, with the Dutch incumbent promising further reforms and his Spanish challenger pointing to his country's economic turnaround. Spain's Luis de Guindos has been seen as the frontrunner for the job, with many believing it is time for the chairmanship to pass to one of the southern countries hardest hit by the euro zone's debt crisis. The race for the Eurogroup position comes as finance ministers struggle to hammer out a deal between Greece and its international creditors to avoid a default at the end of the month, which many fear could lead to a Greek exit from the euro.