* Carrie Lam has served as chief secretary since 2012
* Said she would run in leadership election in March
* If elected, would be first female leader in modern HK history (Recasts with Lam's confirmation of intention to run)
By Venus Wu
HONG KONG, Jan 12 (Reuters) - Hong Kong's number two official Carrie Lam, nicknamed "the fighter", resigned on Thursday to contest the March election to become the financial hub's next chief executive and first female leader.
Lam, 59, has served as the city's chief secretary since 2012 and is known for her no-nonsense approach to overseeing the civil service.
"I told the chief executive in my resignation letter that there is only one reason for me to resign at this juncture, and that is if my resignation is approved by the Central People's Government, I intend to prepare to contest in the upcoming chief executive election," Lam told reporters.
The former British colony returned to Chinese rule in 1997 and its next leader faces the task of reconciling longstanding tensions between Communist Party leaders in Beijing and pro-democracy advocates agitating for universal suffrage.
The city was roiled by street occupations and violent clashes between pro-democracy activists and police in late 2014, while growing calls for independence and self-determination from a disaffected younger generation have alarmed China and stoked mistrust on both sides.
The bespectacled Lam, a career civil servant often appearing in elegant Chinese cheongsam dresses, is seen as one of the frontrunners in the race to lead the territory, which is governed under a "one country, two systems" principle, granting it a high degree of autonomy under Chinese rule.
Respected former Financial Secretary John Tsang, who resigned in mid-December, is also expected to run for the top post. He hasn't made a formal announcement and his resignation has yet to be approved.
Incumbent Beijing-backed leader Leung Chun-ying, whom opinion polls have ranked as one of the most unpopular city leaders, surprised many in December when he said he wouldn't seek a second five-year term.
A committee of 1,200 people, most of them Beijing loyalists, will vet potential candidates before choosing the next leader for the city of 7.2 million people on March 26.
Lam came second in a popularity poll of potential candidates running for the top job, trailing Tsang, according to a Chinese University survey of more than 1,000 people commissioned by the South China Morning Post and released on Thursday.
Lam's potential bid, however, may be complicated by a major public outcry over a planned museum to be built on a prime harbourfront site displaying imperial treasures loaned from Beijing's Palace Museum in the Forbidden City.
While Lam won plaudits for spearheading a potentially world-class institution at the heart of a new district aimed at transforming Hong Kong into a regional arts hub, the deal with Chinese officials behind closed doors was criticised for lacking any public consultation, including her appointment of a prominent architect.
She was also the flag-bearer for a contentious Beijing-backed political reform package that was rejected by pro-democracy lawmakers and seen as a trigger for the months-long, sometimes violent "Umbrella Movement" street protests in late 2014. (Editing by James Pomfret and Nick Macfie)