Banks in the US, receiving billions of dollars in taxpayer bailouts, owe their executives more than $40 billion (£24.31 billion) in pay and bonus deals racked up before they hit the rocks.

The commitments, many not previously been made public, have largely been overlooked in the rush to save the firms from collapse. While the Treasury is putting restrictions on how banks pay top executives in the future, the rules won't cover money that is already owed through "deferred compensation accounts".

Nor have most firms set aside cash or stock for these IOUs, and the money will have to be found out of earnings, says the Wall Street Journal, which revealed the huge debts.

The scale of the fat-cat pay bills is likely to set off a storm of protest among politicians and the public, already incensed at having to hand over billions to cover Wall Street's excesses. The Journal says the money owed is mostly for special executive pensions and deferred compensation, including bonuses, for previous years.

Both Presidential candidates have made the huge bonuses pocketed by the likes of Lehman Brothers boss Dick Fuld a campaign issue.

The Treasury had little comment on the new figures but said it had addressed the issue for the coming year.

A spokesman said: "Every bank that accepts money through the Capital Purchase Program must first agree to the compensation restrictions passed by Congress just last month and every bank that is receiving money has done so."

Its restrictions on fat-cat pay include curbing new golden parachutes and banning tax deductions on pay over $500,000 but it does not address these largely invisible payments.

The practice of deferring compensation and issuing corporate IOUs for executives' pensions is legal and popular with employers, who can put off immediate payment, and employees, who limit their tax bill.

The deferred pay is then treated like a pension fund in hypothetical accounts that often pay high rates of interest.

At mortgage finance giant Freddie Mac, executives earned 9.25% on their deferred-pay accounts in 2007, for example.

These accounts are often well-hidden as few firms report them Goldman Sachs is an exception. The Journal said it calculated them by extrapolating from figures the firms are forced to disclose.

In some cases, banks have inherited other pay liabilities when taking over troubled rivals.

Bear Stearns, for example, owed its executives $1.7 billion at the beginning of the year. The government took over $29 billion in losses to push through a deal in which JPMorgan bought it. The investment bank, led by Jamie Dimon, says it will honour executive pay deals. It adds that the bill has been reduced as much of the payments were in, now deeply discounted, stock.

JPMorgan is also stuck with the bill for executive pay at Washington Mutual, although the Journal says it was impossible to determine the scale of those liabilities.