* Vote could expose faltering ANC grip
* Row over sanitation for the poor
* Opposition DA looking for gains
By Jon Herskovitz
JOHANNESBURG, May 18 (Reuters) - South Africans head to the polls on Wednesday for municipal elections in which squalid unenclosed toilets built for the country's poor have become a potent symbol of local government neglect.
The ruling African National Congress, which has ruled since apartheid ended 17 years ago, is expected to storm to victory given the public esteem it still enjoys for bringing down white-minority rule.
But the ANC and its leader, President Jacob Zuma, could be embarrassed by any gains for the major opposition Democratic Alliance (DA), which runs Cape Town and has campaigned as the party that can deliver municipal services.
What once appeared as a dull race for control of 278 municipalities, including Johannesburg, Cape Town, Durban and Pretoria, has heated up in recent days as a row over unenclosed toilets, whose users are exposed to full public view, has dominated headlines and TV broadcasts.
The ANC scored political points a few months ago when it found the DA had not built walls around public toilets in shantytowns in an area it controlled.
But it came under fire when it was revealed just before the vote to have done the same, with a local ANC official being paid state funds despite the shoddy construction.
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For Factbox on S.Africa since apartheid [ID:nLDE7331TG]
Since Zuma took power in 2009, the ANC has faced violent protests from its traditional base of poor blacks. Many are frustrated with the slow delivery of electricity, sanitation, functioning schools and basic healthcare.
Some are expected to show their anger by either not voting, or doing what was unthinkable a few years ago: casting a vote for the DA, a party once associated with white privilege and now trying to reinvent itself as providing good governance for all.
"This is the first time in the post-apartheid South Africa that our politics appears to be moving toward being about the issues rather than about the identity of the voters," said independent political analyst Nic Borain.
The election may show the ANC is vulnerable, but it could take decades before a viable alternative will challenge it.
"We are too close to the end of apartheid in 1994 to expect a massive transformation of the vote," Borain said.
Some of the key numbers to watch will be any fall in the support for the ANC, which was about 67 percent of the total vote in the last municipal race in 2006, and any gains in support for the DA, which scored about 14 percent in 2006.
Any slips in voter turnout, which was 48.4 percent in 2006, or gains by the DA in major urban areas, would deal a blow to Zuma and could undermine him and embolden his rivals in the highly splintered ruling party. (Editing by Mark Trevelyan)
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