NEW YORK (Reuters) - A government rescue plan has eased investors’ concerns about Citigroup Inc, but mines lurking in the balance sheets of rivals including Bank of America Corp could still tempt short-sellers.

Bank of America, the No. 3 U.S. bank by assets, has loaded up on mortgages as the world’s largest economy wrestles with the worst housing market since the Great Depression.

The Charlotte, North Carolina-based bank further heightened its exposure to home loans by acquiring Countrywide Financial Corp, the largest U.S. independent mortgage lender and agreeing to buy Merrill Lynch & Co, which owns the world’s largest retail brokerage.

If losses on mortgages and other debt securities mount significantly, the bank may see the ratio of equity to risk-weighted assets, known as Tier-1 capital, dwindle to alarmingly low levels.

“I would expect there are more banks who are in dire straits and more who can expect to be helped,” said Michael Farr, president of investment management company Farr, Miller & Washington in Washington, D.C. “The share price makes it look like Bank of America might be next in line,” he said.

Before Monday’s stock market rally, Bank of America shares had lost 52 percent in November alone, making them the second biggest decliner for the month in the KBW Banks index after Citigroup.

Analysts at independent research company CreditSights forecast that in a scenario where the commercial and residential real estate markets really tank beyond banks’ expectations, Bank of America would have a Tier-1 capital ratio of 7.15 percent.

The minimum that regulators seek to consider a bank “well capitalized” is 6 percent, but any ratio near or below 7 percent tends to spook investors.

Bank of America declined comment.

CreditSights also expressed concern about Wells Fargo & Co, which it said would have a Tier-1 capital ratio of 6.98 percent under its worst case scenario. Wells Fargo recently agreed to buy Wachovia Corp.

Under the same assumptions, and before the government’s latest investment, Citigroup would have a Tier-1 capital ratio of 8.64 percent.

Wells Fargo, based in San Francisco, declined to comment.

To be sure, by some measures Citigroup looks worse than Bank of America and Wells Fargo, most notably the ratio of tangible assets to tangible equity, a metric on which some investors have focused.

Citigroup’s tangible assets are about 42 times shareholder equity minus intangible assets, compared with 11 times for Bank of America.

The U.S. banking system is broadly undercapitalized, perhaps to the tune of more than $1 trillion, and the only investor that can bail it out is the U.S. government, analysts said.

“The banks already have an enormous hole to plug, and the recession will make that hole larger,” noted Daniel Alpert, investment banker at Westwood Capital in New York, estimating banks may need to write down $1 trillion more in bad debt, in addition to the roughly $750 billion announced so far.

TOXIC MORTGAGES

Bank of America, through its acquisition of Countrywide, has more than $250 billion in residential mortgages and while it has stopped offering some of the most toxic types of mortgages, chargeoffs in the portfolio are increasing.

Wells Fargo inherited a portfolio of more than $260 billion in consumer loans when it acquired Wachovia, and JPMorgan Chase & Co acquired exposure to some of the most risky classes of mortgages, in addition to its own large consumer loan portfolio, when it bought Washington Mutual Inc.

Still, there are big differences. Critically for Citigroup, investors lost confidence in the company and its management after it failed to buy Wachovia Corp, thereby losing an important potential source of deposit-based funding, analysts said.

“The difference between Citi and the other three is that Citi clearly had more suspect management,” said Mal Polley, chief investment officer at Stewart Capital Advisors in Pittsburgh. “They had not done enough to take the fat out of the system and right the ship,” he added.

But management at Bank of America and Wells Fargo, and even JPMorgan, widely regarded as the bank that has best survived the credit crisis to date, will need to allay investors’ concerns about their capital position as financial conditions worsen.

And if their losses are big enough, or investors fear they will be big enough, Bank of America and Wells Fargo could turn to the same place Citigroup did: the U.S. government.

“I definitely think other companies will need this help,” said Paul Miller, analyst at Friedman, Billings, Ramsey & Co in New York.