China's two biggest banks have each secured preliminary deals involving foreign investments of about $3 billion, the latest wave of money betting that the profit potential offered by reform of China's banking sector outweighs a troubled legacy of lax lending and corruption.

On Tuesday, a group of investors including the investment arm of Goldman Sachs Group Inc., American Express Co. and Allianz AG of Germany signed a preliminary agreement to buy about 10 percent of China's biggest lender by assets, Industrial and Commercial Bank of China, for more than $3 billion, according to a person familiar with the matter.

Meanwhile, Temasek Holdings Ltd., the Singapore government's investment arm, is preparing to invest about $3 billion for about 10 percent in China's second-largest bank by assets, Bank of China, according to a person involved with those talks. That purchase would transform Temasek, which already owns a major stake in China Construction Bank, into the biggest foreign player in China's banking sector.

The two latest deals would bring to more than $15 billion the amount of money foreign investors have agreed to put into Chinese banks since June, though not all the deals have been completed. Bank of America Corp., in mid-June, put $2.5 billion into China Construction Bank for a 9 percent stake, with the option to increase its stake to 19.9 percent. This month, Royal Bank of Scotland Group PLC led a group of investors that included Merrill Lynch & Co. and Hong Kong billionaire Li Ka-shing in a $3.1 billion investment in Bank of China. Last year, HSBC Holdings PLC took a 19.9 percent stake in the Bank of Communications for $1.75 billion.

Underlying the appeal of China's lenders is the potential profit to be earned from the country's rapid economic growth, expected to be 9 percent this year, and the rise of Chinese consumerism. Penetration rates for credit cards and insurance among China's 1.3 billion people are low, and the growing popularity of cars, home ownership and other symbols of middle-class status hold the promise of big growth in consumer loans.

A decade ago, China began to transform its banks from sources of government-decreed lending into commercial entities with professional management so they can better compete when the market is opened to foreign competition at the end of next year. As part of that effort, Beijing has put $60 billion into its three biggest banks to offset bad loans, ordered the improvement of credit-risk systems and put in place audit committees and board structures to try to ensure that management acts in the best interest of the bank.

"Ten years ago, Chinese banks were not commercially run at all," said David Marshall, a banking analyst with the Fitch ratings agency in Hong Kong. But, he said, "it will take many more years before Chinese banks have robust risk-management systems and sound financial profiles."

The downside risks are formidable, with corruption and theft chief among them. Chinese state media reported this month that a former head of Bank of China's listed Hong Kong unit was given a suspended death sentence for embezzlement. In April, the bank revealed a lending scandal that it said cost its Beijing branch about $78 million. The chairman of China Construction Bank resigned in March after allegations of corruption.

Beyond that is the issue of asset quality. The banks themselves aren't very profitable, and "if the economy takes a stumble, the impact on the banks will be disastrous," Marshall said. Concerns about that led Royal Bank of Scotland, the world's sixth-biggest bank by market capitalization, to ask for protection against erosion in the value of its investment when it agreed to its $1.6 billion investment in Bank of China earlier this month, according to a person involved in the deal.

The proposed deal signed Tuesday with the Goldman-led consortium is a preliminary agreement, according to the person familiar with the talks. While the financial terms are still subject to negotiation, this person said that Allianz will put in about $1 billion, mainly through its principal investment group, American Express between $200 million and $300 million and a Goldman Sachs private-equity fund will provide the rest.

Goldman, which will sell part of its stake to other investors, has already profited handsomely from an investment in China's finance sector. In May, Goldman and Morgan Stanley sold their combined 9.91 percent stake in Ping An Insurance Co. for $1 billion, a hefty return on the $35 million each bank invested in 1994.

The planned investment by Singapore's Temasek in Bank of China makes the government-owned company an unlikely leader of foreign investors in Chinese banking.

Temasek said in July it would invest $1 billion into the initial public offering of China Construction Bank, which is expected this year. It is also looking to invest about $1.4 billion in the bank by separately purchasing shares owned by the government, according to a person familiar with the talks. And it has a 4.6 percent stake in China Minsheng Banking Corp., a smaller lender, worth about $190 million.

Temasek was established to manage the Singapore government's holdings in state-owned companies. In 2002, it brought in a new chief executive, Ho Ching. She is married to Lee Hsien Loong, who became Singapore's prime minister last year.

Under Ho, Temasek has gone on a diversification binge, buying stakes in banks across Asia, including Indonesia, India and South Korea. But China is where it has been boldest, committing as much as 10 percent of its $54 billion in assets to Chinese banks and giving it a major stake in two of China's four biggest lenders.

A Beijing bicyclist passes the Industrial and Commercial Bank, which signed a deal with a Goldman-led group.