(Corrects Mahathir's age to 91, from 92)
KUALA LUMPUR (Reuters) - More than two-thirds of readers of a liberal-leaning Malaysian news site have backed former premier Mahathir Mohamad to be prime minister, the portal said on Thursday.
Mahathir, 91, served as prime minister for 22 years, earning a reputation as a no-nonsense authoritarian with little time for dissenters promoting liberal values.
But he has recently emerged as a prominent critic of Prime Minister Najib Razak, a former protégé who last year became ensnared in controversy over a multi-billion dollar financial scandal at a state fund.
Najib has denied any wrongdoing.
Mahathir's criticism of the prime minister has endeared him to voters who in the past would have shunned both of them.
Malaysiakini.com news portal, which is often accused by government supporters of favouring the opposition, found in a poll that 69.9 percent of its readers would support Mahathir as opposition candidate for prime minister.
Malaysia is due to hold a general election next year. The opposition has yet to name its candidate, citing a need to avoid infighting between allied parties.
Malaysia's most prominent opposition politician, Anwar Ibrahim, is in prison serving five years for a sodomy conviction that he says was politically motivated.
Mahathir, who stepped down as prime minister in 2003, was not immediately available for comment.
He told Reuters in an interview in March he had no desire to return as prime minister but would be willing to serve as an adviser.
Malaysia's longest-serving prime minister quit the ruling United Malays National Organisation party last year in response to the graft allegations surrounding Najib.
Mahathir has formed a new party and joined an opposition coalition aiming to oust Najib.
The prime minister has weathered the calls to step down and is expected to call an early election this year to capitalise on disarray within the opposition.
According to the Malaysian Digital Association, which tracks top websites, Malaysiakini is Malaysia's second most popular news website, with nearly 700,000 unique visitors in March.
The portal conducted the survey from May 19 for six days.
About a quarter of the 12,777 people surveyed disagreed with idea of Mahathir for prime minister, it said.
Reporting by Rozanna Latiff; Editing by Robert Birsel