Democratic Alliance (DA) leader Helen Zille has called on her African National Congress (ANC) counterpart Jacob Zuma to step down as his party's presidential candidate in the coming elections.

"Put your ambitions aside and act in the interests of the country and the Constitution by publicly stepping down," she said in an open letter to Zuma on Thursday.

Her call was rejected by the ANC later in the day.

Zille's letter comes a day before Zuma's legal team makes representations to the National Prosecuting Authority (NPA).

Zuma faces charges of fraud, corruption, money laundering and racketeering related to a multibillion-rand government arms deal.

Zille said that should Zuma be elected president without first having been exonerated -- by a court -- of the charges against him, the Constitution would be seriously undermined.

"In fact, I have been reliably informed by senior members of the Bar that your election could be challenged in the Constitutional Court.

"That is because your presidency would create a conflict of interest between your constitutional role as head of state and your status as an accused in a matter that has been brought against you by the state itself."

The NPA has 18 charges pending against Zuma.

"If you do not stand trial on these charges, a pall of suspicion will hang over every move you make and every decision you take in the future," she said.

Responding to Zille's call on its leader to step down, the ANC said it was not going to waver in its support of Zuma "because of misplaced comments by the opposition".

Party spokesperson Brian Sokhuto told the South African Press Association the ANC subscribed to the principle that a person was innocent until proven guilty.

"He [Zuma] has not been found guilty in a court of law."

He said Zuma carried the mandate and aspirations of many people, not just in the ANC, but in the country.

"We support him as the face of the ANC," Sokhuto said.

In her letter, Zille said Zuma might have noticed that in mature democracies, unresolved allegations of impropriety sent politicians into early, and sometimes temporary, retirement.

"Yet, you have chosen to pursue your political career [and presidential ambitions], despite the fact that you have not publicly dealt with the serious and varied allegations the prosecution thinks it can prove against you in a court of law.

"Your trial must go ahead. Once the criminal proceedings are finally over, you can re-enter the world of politics, unless any sentence imposed precludes you from doing so.

"Any vote in Parliament in favour of your election as president is open to legal challenge on the basis that it would be invalid for want of consistency with the Constitution," Zille said.

Zuma's 'poor chance'

Meanwhile court papers lodged on behalf of the National Directorate of Public Prosecutions (NDPP) on Tuesday said Zuma has a "poor" chance at succeeding in his appeal to the Constitutional Court.

"I submit that Mr Zuma's application for leave to appeal to this court is not in the interests of justice because his prospects of success are poor," states George Baloyi, the Deputy Director of Public Prosecutions.

Zuma has lodged an application to appeal against a ruling by the Supreme Court of Appeal (SCA) in January.

The SCA ruling overturned a Pietermaritzburg High Court ruling in September last year, which in effect halted Zuma's prosecution.

The high court ruling also hinted at political interference in the decision to prosecute Zuma, who is the ruling party's presidential candidate in general elections this year.

That part of the high court ruling ultimately led to the axing former president Thabo Mbeki.

The NDPP argues in its papers that Zuma's appeal in the Constitutional Court is pointless.

"The essence of Mr Zuma's complaint is that the NPA should not have taken the decision to prosecute him without first affording him a hearing," contends Baloyi.

"If his intended appeal were to be upheld, it would mean that the NPA would be obliged to afford him a hearing, after which the NPA could still take the decision to prosecute him."

But there would be no need for a further hearing, says Baloyi, because "by the time the intended appeal is determined, the NPA will have considered representations by Mr Zuma concerning his prosecution".

Baloyi says if the NPA decided to continue with his prosecution, this appeal before the Constitutional Court would have just caused another delay.

"If those representations are not successful from Mr Zuma's perspective [i.e. the NPA decides to continue with his prosecution], all the intended appeal [if successful] will achieve is yet another interruption and further delay in this matter in order to facilitate the making, consideration and determination of yet further representations," Baloyi argues. -- Sapa

With acknowledgements to Sapa and Mail and Guardian.