* Ramphele respected anti-apartheid activist
* Cites 'failure of governance' in S.Africa
* ANC still dominant, dismisses party launch (Adds ANC reaction)
By Jon Herskovitz
JOHANNESBURG, Feb 18 (Reuters) - Respected anti-apartheid activist Mamphela Ramphele launched a new political party on Monday to challenge South Africa's ruling ANC, saying self-interested and corrupt leaders were threatening the continent's biggest economy.
Invoking the spirit of Nelson Mandela and the optimism that prevailed at South Africa's first all-race elections in 1994, Ramphele said the dream of the "Rainbow Nation" was dying under the African National Congress (ANC).
"Our society's greatness is being undermined by a massive failure of governance," she said, urging South Africans to "build our nation into the country of our dreams".
Ramphele, 65, faces a formidable challenge. Although political support for the ANC is weakening 19 years after the end of white-minority rule, it remains an unrivalled political machine and commands a nearly two-thirds majority in parliament.
But the medical doctor and former World Bank managing director has the respect of much of the country's black majority as a partner of Black Consciousness leader Steve Biko, who died in 1977 in apartheid police custody.
She was also placed under house arrest for seven years by the apartheid government because of her political work. She has regularly challenged authority and the ANC on its failings.
The new party, which will contest elections due early next year, will be called 'Agang', the Sesotho word for "Let us build".
The ANC "noted" her announcement but said Ramphela's launch speech, outside the Constitutional Court in central Johannesburg, offered nothing new.
The 101-year-old liberation movement also dismissed Ramphele's accusation that it was to blame for income inequality, social violence, failing education and other problems.
"The criticism of the ANC is a failure to acknowledge that many of the challenges were not created by the ANC. It is historical," party spokesman Keith Khoza said.
"Any party that won elections would have faced the same societal issues in education, health, housing and so on."
A group of ANC heavyweights split off in 2008 to form the Congress of the People (COPE) but the party fared poorly in elections the following year and has since all-but imploded amid infighting and wrangling. (Reporting by Jon Herskovitz; Writing by Ed Cropley; Editing by David Dolan and Andrew Heavens)