Federal regulators approved a radical plan to stabilize Citigroup in an arrangement in which the government could soak up billions of dollars in losses at the struggling bank, the government announced late Sunday night.

 

Regulators hope the dramatic action will bolster badly shaken confidence in the once-mighty banking giant as well as the nation's financial system, a goal that so far has been elusive despite a flurry of government interventions to battle the worst global crisis since the 1930s.

 

The complex plan calls for the government to back about $306 billion in loans and securities and directly invest about $20 billion in the company. The plan, emerging after a harrowing week in the financial markets, is the government’s third effort in three months to contain the deepening economic crisis and may set the precedent for other multibillion-dollar financial rescues.

 

Wall Street showed its relief over a move it hopes will help address some of the uncertainty hounding the financial sector. Stocks jumped about 3 percent, extending Friday's big rally.

 

Citigroup executives presented a plan to federal officials on Friday evening after a weeklong plunge in the company’s share price threatened to engulf other big banks. In tense, round-the-clock negotiations that stretched until almost midnight on Sunday, it became clear that the crisis of confidence had to be defused now or the financial markets could plunge further.

 

Whether this latest rescue plan will help calm the markets is uncertain, given the stress in the financial system caused by losses at Citigroup and other banks. Each previous government effort initially seemed to reassure investors, leading to optimism that the banking system had steadied. But those hopes faded as the economic outlook worsened, raising worries that more bank loans were turning sour.

 

President-elect Barack Obama was also working over the weekend to shore up confidence in the rapidly faltering economy. Mr. Obama signaled that he would pursue a far more ambitious plan of spending and tax cuts than he had outlined during his campaign and planned to announce his economic team on Monday. Some Democrats in Congress, meantime, were calling for the government to spend as much as $700 billion to stimulate the economy over the next two years. Federal Reserve Chairman Ben Bernanke was involved during the discussions.

 

Mr. Obama’s expected choice for Treasury secretary, Timothy F. Geithner, the president of the Federal Reserve Bank of New York, played a crucial role in the negotiations on Friday but took a less active role once news of his appointment was circulated. While the initial focus of government officials was to help the embattled company, they may also seek to draw up an industrywide plan that could help other banks.

 

The plan could herald another shift in the government’s financial rescue. The Treasury Department first proposed buying troubled assets from banks but then reversed course and began injecting capital directly into financial institutions. Neither plan, however, restored investors’ confidence for long.

 

Inside Citigroup’s Park Avenue headquarters, the mood was tense. Through the weekend, Robert E. Rubin, the former Treasury secretary and an influential executive and director at Citigroup, held several discussions with Treasury Secretary Henry M. Paulson Jr.

 

Vikram S. Pandit, Citigroup’s chief executive, spoke to regulators and lawmakers. Mr. Pandit also met with Citigroup’s board on Saturday, and there was no indication that they would seek to replace him.

 

Once the nation’s largest and mightiest financial company, Citigroup lost half its value in the stock market last week as the bank confronted a crisis of confidence. Although Citigroup executives maintain the bank is sound, investors worry that its finances are deteriorating. Citigroup has suffered staggering losses for a year now, and few analysts think the pain is over. Many investors worry that it needs more capital.

 

With more than $2 trillion in assets and operations in more than 100 countries, Citigroup is so large and interconnected that its troubles could spill over into other institutions. Citigroup is widely viewed, both in Washington and on Wall Street, as too big to be allowed to fail.

 

Citigroup executives reached out to the Federal Reserve and the Treasury last week as they sought to stabilize the company’s stock. All major bank stocks have been battered in recent weeks, including those of Bank of America, Goldman Sachs, JPMorgan Chase and Morgan Stanley.