By Catarina Demony and Sergio Goncalves
LISBON (Reuters) - Portugal's former infrastructure minister, Pedro Nuno Santos, 46, joined the race on Monday to become Socialist Party leader in an upcoming general election after its current chief and Prime Minister Antonio Costa resigned amid a corruption probe.
Costa, in power since 2015, stepped down last week over an investigation into alleged illegalities in his government's handling of green energy projects. President Marcelo Rebelo de Sousa has called a snap election for March 10.
The resignation also left Costa's job as secretary-general of the Socialist Party (PS) up for grabs, and whoever wins the leadership race will run for prime minister.
Interior Minister Jose Luis Carneiro, 52, was the first to formally announce he was running on Saturday, saying he was "aware of the magnitude of the challenge".
Carneiro, seen as a moderate candidate, served as secretary of state of Portuguese communities in 2015-2019 before being named minister in March 2022.
Although Nuno Santos' popularity was hurt after he resigned in December 2022 in a scandal around a severance payout by state-owned airline TAP, he is seen as the front-runner by many.
Speaking at the PS headquarters in Lisbon, Nuno Santos, from the left wing of the centre-left party, said the Portuguese were aware of his "qualities and flaws" and his "desire to make things happen".
"They also know my mistakes and my scars... those who don't do things and don't make decisions rarely make mistakes," he said as supporters applauded him.
Nuno Santos successfully coordinated support for a previous minority government with the far-left in 2015-2019.
A survey by pollsters Aximage for the newspaper Diario de Noticias showed on Saturday 30% of the Portuguese would prefer Nuno Santos to replace Costa while only 9% would like to see Carneiro at the helm.
Political scientist Adelino Maltez would not predict who was likely to win, describing Nuno Santos as "more communicative and emotional", but highlighting that Carneiro was currently "one of the most popular ministers".
The Socialists are expected to pick a new leader in mid-December.
The first opinion poll after Costa's resignation, released on Friday by Intercampus, showed the PS slumping to 17.9% support from 25.2% in October, while the centre-right opposition Social Democrats (PSD) slipped to 21.8%.
(Reporting by Catarina Demony and Sergio Goncalves; Editing by Andrei Khalip and Andrea Ricci)