Updated from 12:56 p.m. EST

U.S. stocks were soaring Monday after the government announced an aid package for

Citigroup

(C) - Get Report

and President-elect Barack Obama unveiled key members of his economic team.

The

Dow Jones Industrial Average

was climbing 314 points to 8361, and the

S&P 500

was adding 41 points to 841. The

Nasdaq

gained 63 points at 1447.

Over the weekend, the Treasury, the Fed and the Federal Deposit Insurance Corp. announced they would move to

prop up Citigroup

in part by investing $20 billion of the $700 billion Troubled Asset Relief Program in Citi shares. The large stake follows an earlier $25 billion TARP investment from the government. The agencies also said they will guarantee against up to $306 billion in potential loan losses by the bank.

Shares of Citi had dropped 60% in the past week on concerns about its ability to survive the credit crunch intact and on Friday, Citi executives reportedly denied speculation that the bank would sell all or part of itself to raise capital. On Monday, the stock rebounded, gaining more than 50% on the bailout news.

Government aid for Citi is reassuring in that it shows that the government is willing to help vital institutions stay afloat as the credit crisis continues, said Richard Sparks, senior equity analyst at Schaeffer's Investment Research. However, the need for intervention underscores challenges faced by other large institutions, he said.

Investors were also heartened by the incoming administration's efforts to bolster the faltering economy. The transition team of President-elect Barack Obama said on Sunday it is working on an

economic-stimulus plan

to help avert the worst of an emerging downturn. Details include possibly allowing President Bush's tax plan to remain in place and legislation that would add or replace 2.5 million American jobs.

Speaking in Chicago, President-elect Barack Obama on Monday confirmed earlier reports that he would nominate New York

Federal Reserve

chief

Tim Geithner

to run the Treasury Department and tap former Treasury Secretary Lawrence Summers to head the National Economic Council. Media reports of Geithner's nomination had on Friday coincided with a late-rally in the major averages.

Obama also announced Christina Romer would lead his Council of Economic Advisers and Melody Barnes would direct the Domestic Policy Council. Romer is an economist at the University of California at Berkeley, and Barnes is the former executive vice president for policy at the Center for American Progress.

In a separate speech in Washington, President Bush said that he and Obama are working together to develop additional policies to prevent further economic deterioration.

Sparks of Schaeffer's said that the Obama team's quick movement to put a team in place and develop a plan of action helps remove some uncertainty related to the presidential transition, but "The biggest uncertainty is how widespread, and how hard-hitting, will the aftermath of the crisis be."

Michael Strauss, chief economist and strategist at Commonfund, said that the current climate warrants aggressive fiscal and monetary policy, as well as initiatives that encourage trade to continue. He said that successful stimulus would probably require dedication by the government of about 2% to 4% of GDP. "At least we're taking some steps in the right direction," he said.

Financial institutions continued to feel shocks related to the credit crisis. News of the Obama plan came after three banks, including

Downey Financial

(DSL) - Get Report

, failed on Friday.

Pessimism about the future of other U.S. companies persisted, as

analysts

at Citigroup cut their price target for the S&P 500 to 850, and cut their 2009 target for the index to 1200.

The market's recent upward movements are to be expected, given a broader downtrend, said Sparks of Schaeffer's. "I don't know if I would at this point call

the recent rally anything important or even significant."

The troubled automakers continued to make headlines, as

Bloomberg

reported that

General Motors

(GM) - Get Report

, which along with

Ford

(F) - Get Report

took large hits last week as they failed to secure a bailout from Congress, is trying to reduce its debt and delay a large payment to a union health fund. The report indicated that such a move is an effort to meet conditions that the company retool its business if it hopes to get government money.

On Saturday, a report by

The Wall Street Journal

, citing people familiar with the matter, said that GM's board was now open to a possible bankruptcy filing. The board's reported position puts it in opposition to CEO Rick Wagoner, who has repeatedly stressed that he was not considering bankruptcy protection.

As to corporate earnings,

Campbell Soup

(CPB) - Get Report

saw increasing fiscal first-quarter earnings per share but said a stronger dollar would hurt international sales.

Xerox

(XRX) - Get Report

also affirmed that it has sufficient capital and offered profit guidance that was in line with analysts' expectations.

In the merger arena,

Johnson & Johnson

(JNJ) - Get Report

announced it would buy

Omrix Biopharma

(OMRI)

for $438 million, or $25 a share, in cash.

Among other deals,

Alpharma

(ALO) - Get Report

agreed to be bought by

King Pharmaceuticals

(KG)

for $1.6 billion in cash.

Eli Lilly

(LLY) - Get Report

completed its purchase of

ImClone

.

Looking at the day's economic data,

October existing-home sales

from the National Association of Realtors came in at an annual rate of 4.98 million, down from 5.14 million in September and slightly below economists' forecasts.

Ian Shepherdson, chief U.S. economist for High Frequency economics, wrote in an email that the National Association of Retailers believes about 45% of home transactions are foreclosure-related. "The private market is still very weak indeed, and the next few months represent a severe test in the wake of the plunge in stocks and consumer confidence," he said.

Shifting to commodities, crude oil was climbing $4.34 to $54.27 a barrel. Gold gained $27.70 to close at $819.50 an ounce.

Longer-dated U.S. Treasury securities were falling in price. The 10-year was down 1-6/32, yielding 3.34%, and the 30-year was off 25/32 to yield 3.73%. The dollar was weakening against the euro and pound but rising vs. the yen.

Abroad, European exchanges logged huge gains. The FTSE in London was up 9.8%, and the DAX in Frankfurt rose more than 10%. In

Asia

, Japan's Nikkei was closed for a holiday. Hong Kong's Hang Seng index finished with losses.