WASHINGTON – Congressional investigators have doubled the estimate of cash Saddam Hussein generated from subverting the oil-for-food program of the United Nations. They told a Senate subcommittee yesterday that at least $21 billion was secured by the Iraqi dictator from a range of illegal schemes, including oil smuggling and kickbacks.

Previous studies by American government agencies of illicit revenue flows concluded that Mr. Hussein’s regime generated $10 billion from sanctions busting from 1991 to 2003. Armed with more documents and using different methodologies, investigators told the Permanent Subcommittee on Investigations that more oil was smuggled out of Iraq than had been calculated before.

In oil smuggling alone, Mr. Hussein is now thought to have profited to the tune of $13.7 billion. As with other schemes designed to subvert the international sanctions on his country, the investigators said, the connivance of corrupt U.N. officials and companies that were protected by members of the Security Council, such as Russia and France, was needed for Iraq to game the system.

Speaking before yesterday’s subcommittee hearing, the chairman, Senator Coleman of Minnesota, warned journalists against considering the estimate of $21 billion a final one. “This is an evolving figure,” he said.

Likening his committee’s investigation to peeling an onion, Mr. Coleman said: “We just keep uncovering more layers and more layers.”

The Republican also blasted the United Nations for its failure to cooperate with congressional probes into the oil-for-food program, a scheme that allowed Baghdad to sell oil in exchange for food, medicine, and other humanitarian goods. He disclosed that at the weekend he had a phone conversation with Secretary General Annan, who appeared to indicate the U.N. would now be more helpful.

But the Minnesota senator complained about the failure of the U.N. to provide documents, including 55 oil-for-food internal audits, and access to international officials. He said “constructive action” was needed from the world body as Congress seeks to get to the bottom of why when “folks there knew something was awry, they did not act on it.”

“We have to find out how this massive fraud was able to thrive for so long,” Mr. Coleman said.

After details of alleged corruption surfaced earlier this year, Mr. Coleman’s panel launched one of several congressional probes into alleged illegal profiteering in the oil-for-food program. A former chairman of the Federal Reserve, Paul Volcker, is heading an investigation set up by the United Nations, but Mr. Coleman and other American lawmakers said it is proceeding at a glacial pace and noted it lacks subpoena power.

In testimony yesterday before the panel, investigators also raised a previous estimate of $4.4 billion in oil-for-food kickbacks by $200 million and said Mr. Hussein’s regime made $2.1 billion more by selling flawed and substandard imported goods at inflated prices.

Fleshing out details of kickbacks, allocations of Iraqi oil and illegal surcharges on oil sales, investigators presented documents demonstrating that Mr. Hussein and high-level colleagues in his regime were personally involved in the oil-for-food corruption.

Documents released also cast further light on how the former Iraqi dictator rewarded senior officials in foreign governments and at Turtle Bay by giving them oil vouchers that they could sell on the world oil markets, making considerable profits for themselves in the process.

The political use of oil vouchers by Mr. Hussein was first detailed earlier this fall in a report by the top American arms inspector, Charles Duelfer.

“Saddam Hussein attempted to manipulate the typical oil allocation process in order to gain influence throughout the world,” a counsel to the subcommittee, Mark Greenblatt, said yesterday.

“Rather than giving allocations to traditional oil purchasers, Hussein gave oil allocations to foreign officials, journalists, and even terrorist entities, who then sold their allocations to the traditional oil companies in return for a sizable commission,” he said.

In his testimony, Mr. Greenblatt listed as oil-voucher recipients Benon Sevan, who headed the U.N. office overseeing the oil-for-food program; a Russian politician, Vladimir Zhirinovsky; a former French interior minister, Charles Pasqua; a British Labour parliamentarian, George Galloway, and a Syrian journalist, Hamidah Na’na.

Mr. Zhirinovsky and Mr. Galloway were vociferous advocates for the lifting of U.N. sanctions. Investigators said the Iraqi government allocated 80 million barrels of oil to Mr. Zhirinovsky, and they released a copy of a letter written by the Russian inviting an international oil company to Moscow to negotiate to buy oil allocated to him.

The Russian, along with other foreign politicians named in recent weeks as oil voucher recipients, denied any wrongdoing. Last month, Mr. Annan said he didn’t believe the Security Council had been influenced or bought in any way by the ousted Iraqi dictator.

Terrorist groups listed by panel investigators as participating in the Iraqi oil bounty were the Popular Front for the Liberation of Palestine and the Mujahadeen Khalq of Iran. Mr. Duelfer later told the committee, however, that in his probe he had not come across evidence showing that money made from subverting sanctions had gone to terrorist organizations. “We didn’t see anything obvious,” he said.

Mr. Coleman said the “weakness in the oil-for-food program raises serious questions about the United Nations’ ability to enforce sanctions and administrate humanitarian aid programs in the future.”

He also pointed to the recent surfacing of allegations that some of the money raised by the sanctions-busting may be going now to finance “the Iraqi insurgency and terrorist activities in Iraq and elsewhere.”

The Senate subcommittee’s ranking Democrat, Carl Levin of Michigan, defended the United Nations, saying, “For the most part, the U.N. sanctions achieved their intended objective of preventing Saddam from rearming and developing weapons of mass destruction.”

Mr. Levin added: “Sanctions are a club which could have an impact, as they apparently are doing today in Iran. It is useful to learn from the Iraqi experience in which sanctions basically achieve their goals but were weakened in a number of ways, so we can make sanctions work as effectively as possible.”