Vikram Pandit, the new chief executive of Citigroup, has put his bank under further financial strain by bringing $49 billion (£24 billion) worth of high-risk off-balance sheet investments onto its books just as new analysis predicts it will need to take a $30 billion writedown on its loan portfolio next year.

In his first decisive move as Citigroup’s leader, Mr Pandit pledged to provide the necessary funds to keep afloat seven so-called structured investment vehicles (SIVs) - independent debt-financed entities – that the bank runs and is ultimately responsible for.

These kind of opaque funds are finding it virtually impossible to refinance their debt as the value of their mortgage-related securities declines. Many are being forced into a fire sale of assets to maintain their capital base, which is pushing prices down further.

The US Treasury is working with Citigroup, Bank of America and JP-Morgan Chase to set up a $100 billion fund to prop up prices by buying assets from the SIVs.

However, in what may prove an embarrassing failure for Henry Paulson, the US Treasury Secretary, Citigroup’s decision to back its SIVs has taken the already struggling bailout fund to the brink of collapse. It emerged last week that the fund had scaled down its ambitions to less than half the original target because it could not attract enough banks to participate in the scheme.

Citigroup’s move, which came despite repeated assurances that it would not bring the SIVs onto its balance sheet, removes the key beneficiary of the bailout fund, since the bank had the largest exposure to the vehicles on Wall Street.

Analysts said that despite Citigroup’s assurances that it “continued to support [the fund’s] formation”, it is unlikely to take its role as a key architect of the fund so seriously now that it will no longer require its services.

Citigroup has already announced that it expects to lose about $15 billion this year from declines in the value of sub-prime related investments.

It is expected to suffer further writedowns after taking the SIVs onto its books because of their exposure to bonds, backed by high-risk home loans, that are rapidly declining in value after a surge in defaults on the underlying mortgages.

But the bank is likely to suffer much larger writedowns next year, as defaults on mortgages, credit card debt and car financing are set to soar, according to new research by Institutional Risk Analytics, a US consultancy that examines banks’ balance sheets and assesses their financial risks.

Citigroup is expected to write down the value of its $740 billion loan portfolio by about 1 per cent, or $7.4 billion, this year as a result of defaults. In 2008, the write-offs will probably rise to about 4 per cent ($30 billion) or even 5 per cent ($37 billion), according to Chris Whalen, managing director of Institutional Risk Analytics. Mortgages make up about $250 billion of Citigroup’s loans, while credit cards account for a further $100 billion.

Mr Whalen said: “So far, the banking writedowns have been based on valuations of bonds and other investments. Next year it will be down to credit defaults in everything.”

A recent $7.5 billion cash injection by the Abu Dhabi Government will not be nearly enough if Citigroup wants to maintain its present credit rating. Instead, it will need to raise a further $15 billion to $20 billion to preserve its capital base, Mr Whalen said.

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