* March seen as provocation to goad ANC
* Stones and petrol bombs thrown
* DA trying to shake its "white party" image
By Tiisetso Motsoeneng
JOHANNESBURG, Feb 12 (Reuters) - South African police fired rubber bullets on Wednesday at stone throwing supporters of the ruling ANC who tried to confront members of the opposition Democratic Alliance party as they marched in central Johannesburg.
The incident is a sign of rising tensions in South Africa before general elections on May 7, which are seen as the biggest political test yet for President Jacob Zuma and his African National Congress (ANC), which has been in power for 20 years since the end of white apartheid rule.
Police, between the lines of rival supporters, opened fire briefly at ANC members clad in the party's yellow T-shirts.
A police spokesman said petrol bombs were also thrown at officers who responded with stun grenades as well as rubber bullets.
Four people - wearing t-shirts bearing the ANC logo - were subsequently arrested for public violence and illegally carrying dangerous weapons during the march, police said.
Thousands of supporters from both parties were brought in by bus; the DA to march in what it said was a protest about high rates of unemployment in Africa's largest economy and the ANC to defend its headquarters in Johannesburg.
After the brief clash with police the marchers turned around and the protest ended, with DA members saying they had decided to call things off to prevent further violence.
Commentators have viewed the march by the DA, the country's biggest opposition party, as an action or provocation deliberately designed to expose what the opposition says is the ANC's intolerant nature.
"Will every voter now get the point about what an undemocratic and violent and intolerant organisation the ANC is," DA leader Helen Zille told local TV news channel eNCA.
"We knew we were not getting to our end destination from the start, because the ANC came with missiles, petrol bombs, bricks and stones. I was amazed that the police allowed them to do that," she said.
The DA is trying to shake its image as a party devoted to the interests and privileges of the white minority and almost all of the marchers clad in its blue shirts on Wednesday were black, drawing scorn from ANC supporters.
ANC spokesman Jackson Mthembu condemned the DA march.
"It cannot be a wise step for any party to want to march to another party office, very ill informed, very dangerous, very risky, because we share nothing in common with the DA, how can you march ... to the revolutionary house," he said.
Sipho Mkhwanazi, a 40-year-old ANC supporter, was equally ciritical of the DA.
"Those poor black people who were marching today possibly got paid to come here and be the face of the DA."
The DA's attempts to broaden its demographic appeal have suffered some recent setbacks.
Prominent black anti-apartheid activist Mamphela Ramphele last week backtracked on a brief pledge to run for president for the DA, frustrating the party's push to win more black votes in the election.
The ANC is expected to easily extended its two-decade rule but with a reduced majority as millions of black South Africans remain mired in poverty and frustrated with the slow pace of change and economic transformation.
Still, South Africa remains a very different place, a point highlighted by the stark contrast between Wednesday's march and one from 20 years ago, just ahead of the elections that brought Nelson Mandela to power as the country's first black president.
In that incident, thousands of members of the Zulu-based Inkatha Freedom Party marched on the ANC's Johannesburg headquarters and security guards opened fire with live ammunition, killing 19 people.