* Zuma under pressure after anti-graft watchdog report
* ANC stalwarts aim rare criticism at leader
* Ruling party expected to win in May 7 election
By Joe Brock
JOHANNESBURG, March 31 (Reuters) - South African President Jacob Zuma has denied any wrongdoing over a $23 million state-funded security upgrade to his private home, in his first public response to allegations he had benefited unduly from the "excessive" spending.
Public Protector Thuli Madonsela, South Africa's top anti-corruption watchdog, accused Zuma this month of conduct "inconsistent with his office" and said he should pay for some of the renovations at his Nkandla home that included a chicken run and a swimming pool.
However, during campaigning near Cape Town on Sunday for a May 7 parliamentary election, the 71-year-old president brushed aside the criticism.
"They go around and say 'This fella used public money'. I am not guilty. There is no case against me," he said in comments widely reported in the domestic media. "I did nothing wrong. I did not do anything."
Zuma spokesman Mac Maharaj described the reported remarks as "off-the-cuff comments".
The Democratic Alliance, the main opposition party, has filed corruption charges against Zuma with the police, although the party's calls for his impeachment look certain to fail, legal experts say.
Zuma's African National Congress (ANC) is expected to sweep to victory in the election but the scandal is exposing rifts within the former liberation movement, which has ruled South Africa since the end of apartheid in 1994.
Public criticism from within the party is extremely rare, but in the last 10 days a slew of respected ANC figures have questioned the morality of the upgrades and expressed wider concerns about creeping corruption in Africa's biggest economy.
"Taxpayers should not pay for a swimming pool at any individual's house, regardless of who they are," former finance minister Trevor Manuel said.
Archbishop Desmond Tutu, one of Zuma's harshest critics, said Madonsela's report had revealed "stark fault lines" within the ANC and urged Zuma to "do the right thing".
Former president Thabo Mbeki also described it as worrying, although ANC Secretary General Gwede Mantashe and other Zuma acolytes in the party have leapt to his defence.
The upgrades have also prompted outrage from some of South Africa's 53 million people ranging from calls for Zuma's resignation on radio phone-ins to satirical online videos.
One spoof music video entitled "Nkandla style" has recorded a quarter of a million hits on YouTube, replacing lyrics from the 2012 South Korean mega-hit "Gangnam Style" with digs at Zuma's lavish homestead in rural KwaZulu-Natal province.
As the party that freed South Africa from white-minority rule, the ANC is almost certain to win the May 7 election and then to re-elect Zuma for a second five-year term as president.
But the ANC's share of the vote has been declining since 1994 amid frustration over the slow pace of social change.
If it wins less than 60 percent, analysts say senior anti-Zuma figures in the 101-year-old movement could force him to take the blame and push for his removal.
"We think that a rescue mission by the party's 'old guard' is now more likely and that it might successfully manage to shift Mr Zuma aside by around 2016," independent political analyst Nic Borain said.
Zuma, a polygamous Zulu traditionalist, ousted Mbeki as ANC leader in 2007 and became president in 2009. Throughout his political career, he has been dogged by scandals ranging from rape - of which he was cleared in 2006 - to corruption. (Editing by Ed Cropley and Gareth Jones)