The presidential aspirations of South Africa's second-highest elected official, Jacob Zuma, suffered a serious blow Thursday when a court found one of his close friends guilty of soliciting an $80,000 bribe on Zuma's behalf and enjoying a "generally corrupt" relationship with him.

The High Court in Durban did not consider any charges against Zuma, the deputy president, but the closely watched trial of his former financial adviser, Schabir Shaik, has been viewed here as crucial to the chances of the popular and charismatic Zuma becoming South Africa's next president. President Thabo Mbeki is expected to step down when his second term ends in 2009.

The ruling was immediately followed by calls from several opposition parties for Zuma, 63, to resign. Most political commentators agreed that Zuma's chances to become president were damaged if not doomed by the conviction.

"He's finished," said Xolela Mangcu, a political analyst and newspaper columnist. "There is no way he can be president of this country."

Shaik, 48, repeated claims of his own innocence in the hours after the ruling and was released on bail of $16,000 while he awaited sentencing, scheduled for Friday. "I walk in the light of my Lord. . . . I am innocent," he said, according to news service reports.

Zuma, who was traveling on official business in Zambia, declined to comment while he studied the ruling, according to a statement issued by his spokeswoman. In the past, he has publicly maintained his innocence.

Judge Hillary Squires, reading a ruling that aired on national television over the past three days, said Shaik had made illicit payments totaling $180,000 to Zuma over several years to get his help winning government contracts. The judge also ruled that Shaik requested that a French arms company provide Zuma with a bribe of $80,000 a year in exchange for his help in thwarting a corruption probe.

Shaik could be seen grimacing, wincing and shaking his head as the judge read the ruling, which resulted in convictions on two counts of corruption and one of fraud.

"The case is convincing and really overwhelming," Squires said during his reading of the ruling. He also said there was compelling evidence of "a readiness in both Shaik to turn to Zuma for help and Zuma's readiness to give it."

The head of the prosecuting authority said in August 2003 that there was "a prima facie case of corruption" against Zuma as well, but he declined to file charges because he said there was not enough evidence to secure a conviction.

There was speculation throughout the trial that prosecutors would reconsider their decision not to charge Zuma if they won the case against Shaik. After the ruling, a spokesman for the prosecutors declined to comment on whether charges against Zuma would be forthcoming.

Even if there are no new charges, Zuma was portrayed by witnesses as a man in poor command of his own finances and frequently in need of cash to pay for a luxury home and other extravagances.

Many activists within Zuma's party, the African National Congress, have in recent months continued to express their support for him, saying he should become the party's nominee for president despite the corruption trial. The party, which led the decades-long fight against apartheid, took control of the government in 1994 and has dominated South African politics since.

Zuma's strongest support has been among South Africa's formidable labor movement, which is a partner with the ANC in Mbeki's governing coalition. News services reported that a spokesman for the Congress of South African Trade Unions said of Zuma: "He has not been on trial nor charged or convicted of any offense. So we cannot assume that anyone is guilty before he or she has been given a chance to defend him or herself."

Zuma had a modest upbringing and joined the liberation struggle instead of going to school for a formal education. He and Shaik were allies in the liberation struggle and are long-standing friends.

Shaik helped funnel money to the ANC during the years when it was banned by the South African government and operating largely from bases in other countries.

Schabir Shaik, former financial adviser to Deputy President Jacob Zuma, leaves court after being convicted in bribery case.