Indignant Supreme Court judges on Tuesday demanded to know why $60 million in the suspect gains of President Asif Ali Zardari had been given back to offshore companies in his name rather than returned to the national treasury, where they said it rightfully belonged.

The barrage of questions directed at flustered anti-corruption officials was the latest round of embarrassment for Zardari. He is fighting for his political life as the court hears arguments about the legality of an amnesty decree that was devised in 2007 with the help of the United States and Britain as part of a deal to engineer the comeback of Zardari's wife, former Prime Minister Benazir Bhutto, after years in exile.

The decree, which dismissed past corruption allegations, is likely to be declared unconstitutional by the Supreme Court in the coming days. Such a ruling would further weaken Zardari, Washington's chief civilian partner in Pakistan, and perhaps set the stage for his eventual downfall, legal experts and politicians say.

Zardari was a primary beneficiary of the amnesty decree, and though he enjoys immunity from prosecution as president, opponents are planning recourse through the courts to overcome that immunity, lawyers said.

Zardari became president eight months after his wife was assassinated in December 2007. He had served 11 years in jail on charges of corruption and murder that he and his lawyers have always insisted were politically motivated.

Zardari's presidential spokesman, Farhatullah Babar, this week reiterated the position that the corruption charges were unfounded. Zardari and his lawyers say he was never convicted. But whether or not he was convicted remains in question, because he did not appear at a past court hearing, and the issue may yet become central to his future in the presidency, legal experts said.

The hearings that began last week on the amnesty decree, known as the National Reconciliation Order, have served to expose Zardari all over again as a "man widely perceived as corrupt," the leading newspaper, Dawn, said in an editorial.

In one document presented to the court by the National Accountability Bureau, the government office that oversees corruption cases, Zardari was alleged to hold $1.5 billion in assets, including land and overseas bank accounts.

Babar, the presidential spokesman, described the document as wildly inaccurate.

The $60 million that the judges zeroed in on Tuesday represented money that the bureau said in 2003 documents had been placed in a Swiss bank account by Zardari and Bhutto.

An official of the bureau told the court on Tuesday that $13 million represented illegal commissions Zardari received from two Swiss companies, Cotecna and Societe Generale de Surveillance, after they were awarded a contract for pre-shipment inspections for imports to Pakistan.

The remaining $47 million, the official contended, represented illegal commissions for other contracts awarded to foreign companies when Zardari was a Cabinet minister during Bhutto's time as prime minister.

The $60 million was frozen in Switzerland while court cases were brought against Zardari and Bhutto in the early days of the government of President Pervez Musharraf. The money was apparently returned to offshore bank accounts in Zardari's name after the amnesty decree was imposed by Musharraf in November 2007.

Chief Justice Iftikhar Muhammad Chaudhry on Tuesday repeatedly asked who had authorized the money's return to the accounts. The officials from the accountability bureau, now considered a powerless entity that answers to the current government, had no answers.

Chaudhry ordered the former attorney general under Musharraf, Malik Muhammad Qayyum, to appear before the court. Qayyum did not have a direct answer to that question either, but he did say he had acted on the authority of Musharraf to have the cases against Zardari withdrawn.

Zardari is struggling to maintain his authority under pressure from the military and a vocal section of the news media. The Pakistani army in effect accused him of attacking its interests after he supported a Washington aid package that included provisions calling for greater civilian control over the military.

Afraid of becoming the target of a terrorist attack, the unpopular Zardari rarely leaves the presidential building, where he has remained for much of the last 10 days as the Supreme Court has whittled away at his authority.

Zardari has been banking on presidential immunity to save his position. But lawyers fighting the legality of the amnesty decree say that once the decree is declared null and void, Zardari will be exposed to legal challenges on his eligibility as a candidate for the presidency.

According to Pakistani law, presidential candidates are not permitted to have had any prior convictions.

Some Pakistani lawyers say that because Zardari failed to appear when he was called before the High Court in Lahore after he was released from jail in 2004, he is considered an absconder, a status that is enough, they say, to disqualify him as a presidential candidate.

But that issue remains unresolved, and Babar, the presidential spokesman, said Zardari had no convictions.

Lawyers also contend that a 2003 money-laundering conviction of Zardari by a Swiss magistrate, which Zardari and Bhutto appealed, was enough to disqualify him.

Once the Supreme Court rules on the amnesty, lawyers will file petitions in "a matter of days" to challenge Zardari's eligibility as a presidential candidate, said Salman Akram Raja, a lawyer who has argued against the validity of the amnesty.

In the case against amnesty, he represents Mubashir Hassan, the leader of a breakaway faction of Zardari's Pakistan Peoples Party and a staunch opponent of the president.