* ANC on track for big May 7 majority, poll says
* Zuma takes personal knock from Nkandla scandal
* Opposition DA building support to 23 percent
JOHANNESBURG, April 20 (Reuters) - The African National Congress (ANC) is on course to win nearly a two-thirds majority in May 7 elections, a poll showed on Sunday, confounding analysts who had predicted a fall in support for South Africa's ruling party 20 years after the end of apartheid.
The poll, published by South Africa's Sunday Times newspaper, said the ANC was likely to win 65.5 percent of the vote, only a shade lower than the 65.9 percent it won at the last national elections in 2009.
The survey was conducted on April 4, after Public Protector Thuli Madonsela - South Africa's top anti-corruption watchdog - published a damning report into a $21 million state-funded security upgrade to President Jacob Zuma's private home.
Madonsela judged that Zuma had benefited unduly from the upgrades, which included a swimming pool, chicken run and amphitheatre at his residence at Nkandla in rural KwaZulu-Natal, and should pay back some of the money.
While overall support for the ANC remained largely unaffected by the Nkandla scandal, the poll said Zuma's personal approval ratings had slipped to 62 percent from 65 percent before Madonsela delivered her findings.
The poll also showed that the Democratic Alliance, the main opposition party that already governs the Western Cape province, was on track to build its national support from 16.6 percent in 2009 to 23.1 percent this year.
It put support for the Economic Freedom Fighters, a radical leftist party founded last year by expelled ANC Youth League leader Julius Malema, at 4 percent.
The ANC has presided over strong economic growth since the end of apartheid in 1994, but Zuma's first term in office has been rocky.
The economy slipped into its first post-apartheid recession in 2009 and has struggled to regain the growth rates it logged before the global financial crisis.
The government is expecting economic growth this year of 2.7 percent, way below the levels needed to make any in-roads into 25 percent unemployment.
The police killing of 34 striking miners at Lonmin Marikana platinum mine in 2012 also drew widespread criticism, with many South Africans accusing the ANC-controlled police force of apartheid-style brutality.
Analysts had also expected the so-called 'Born Frees' - young South Africans with no first-hand experience of white-minority rule - to withhold their support for the ANC, which still uses its defeat of apartheid as its main draw card.
However, Election Commission figures show that only one in three voters aged 18-19 has registered to vote.
The poll, conducted by Ipsos, surveyed 2,219 voters nationwide. (Reporting by Ed Cropley; Editing by Hugh Lawson)