CAPE TOWN (AFP) -- Cape Town's mayor says vigilance will be needed to sustain democracy in South Africa after bruising battles with the ANC in her first year leading the sole bastion of opposition to the ruling party.

"So far, we have passed the test," Helen Zille said in an interview with AFP ahead of the March 15 anniversary of her installation as mayor. "If they had an opportunity to get me out tomorrow they would, by any means. I've got to be eternally vigilant. But the price of freedom is eternal vigilance."

Her election a year ago marked the first time the African National Congress had lost control of a major municipality since the end of the apartheid era of whites-only rule in 1994.

Since then, Zille has endured numerous attempts on her mayorship, including a move late last year by the minister of local government in the Western Cape province, Richard Dyantyi, to change Cape Town's governance model to oust her.

That ANC officials could contemplate such tactics to retain control left opponents and analysts questioning the extent of its commitment to democracy.

Zille credits President Thabo Mbeki with ordering the central government intervention that caused her multi-party coalition to survive. "This was a sign of basic respect for democratic principles at the heart of the ruling party."

But she was hopeful rather than confident that such principles would continue to prevail.

"It obviously depends on who succeeds President Mbeki. We cannot be too relaxed about it." Mbeki steps down after two terms in 2009.

Zille herself is widely expected to announce her candidacy for the leadership of her party, the main opposition Democratic Alliance, as incumbent Tony Leon retires in May.

Being opposition leader would require constant vigilance against the "Zanufication" of South Africa, she said -- referring to the economic and political crisis engulfing neighboring Zimbabwe under its ruling ZANU-PF. "It is very important for our democracy that the ANC learns to lose elections."

Having lost the municipal poll in Cape Town last March, the ANC's subsequent city "power grab" had been the litmus test for South Africa's democracy but not everybody on the ruling party had learnt the lesson, said Zille.

Another challenge for the country was voting patterns based on racial identity rather than policies and issues -- especially among blacks, said Zille.

"Everyone is deeply scarred by apartheid, but I don't think that anybody is more scarred than black South Africans. "It's going to take a long time before they believe that a white person can really act in their best interests and before they really trust that our commitment is to do that."

Ongoing racial division would also affect the DA's leadership race in which one of the contenders, Joe Seremane, was black.

"If we don't vote for Joe people will say its obvious the DA didn't want a black leader, they won't say: 'are the characteristics the right characteristics for a leader?" said the mayor.