NEW YORK (AP) _ Shares of national banks mostly fell Tuesday on more signs of weakness in the financial sector.American Express Co. won approval late Monday from the Federal Reserve to become a commercial bank as it looks for new ways to fund its business. The status will allow the credit card giant to accept deposits and permanently access government financing that's been used by other banks amid the credit crisis.

Citigroup Inc., meanwhile, became the latest big bank to announce sweeping efforts to try and curtail losses from souring mortgage loans. The New York-based bank said it is imposing a moratorium on most foreclosures as part of a series of initiatives aimed at helping at-risk borrowers stay in their homes.

Additionally, over the next six months, Citi plans to reach out to 500,000 homeowners who are not currently behind on their mortgage payments, but who are deemed as potentially needing assistance to keep current with their payments. This represents about one-third of all the mortgages that Citigroup owns, the bank said.

JPMorgan Chase & Co. and Bank of America Corp. have also become more aggressive in modifying loan agreements in the face of mounting defaults and plunging home values.

Citi shares dropped 48 cents, or 4.3 percent, to $10.73 in morning trading. Earlier in the session, shares fell as low as $10.65 — their lowest point in 13 years.

JPMorgan slipped a dollar, or 2.8 percent, to $35.42, while Bank of America dipped 87 cents, or 4.5 percent, to $18.61.

In a note to clients Tuesday, Robert W. Baird & Co. analyst David George reiterated an "Outperform" rating on Wells Fargo & Co. following the bank's $12.6 billion capital raise, which will be used to help fund the company's planned acquisition of Wachovia Corp.

"We view the stock's recent weakness as an attractive buying opportunity, and continue to believe the Wachovia deal has significant strategic and financial merit," George wrote in a note to clients.

George trimmed his 2009 earnings estimate to $2.15 per share from $2.30 per share. Analysts polled by Thomson Reuters, on average, forecast a profit of $2.06 per share in 2009.

Stifel, Nicolaus & Co. analyst Christopher Mutascio also cut his 2009 estimates on Wells Fargo to $2.10 per share from $2.35 per share.

Wells Fargo said Monday that the underwriters of its common stock offering exercised their overallotment option, resulting in total proceeds of $12.6 billion.

Wells Fargo shares gained 28 cents to $28.92. Wachovia rose 9 cents to $5.57. For more information check out the calculators section located at BankingMyWay.com .

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