So it was in the United States. To allow people to buy homes they really could not afford, banks offered mortgages with artificially low monthly payments in the early years. When home prices fell, the mortgages blew up.

So, too, it was in Hungary, where home mortgages were relatively rare until the banks made it possible for buyers to avoid high interest rates, but with a big risk.

Mortgages denominated in foreign currencies became wildly popular, because that way borrowers could get low interest rates, and thus afford to buy homes that would otherwise be out of reach. But then the local currency, the Hungarian forint, plunged in value, and homeowners faced rapidly rising monthly payments. They owed more forints than they had borrowed.

In the United States, the sanctity of contracts has generally prevailed. The banks have been forced to pay multibillion-dollar penalties for bad behavior, but that does little for the anguished homeowners.

In Hungary, the populist government has decided it is the banks — mostly foreign-owned — that should suffer. Under a new law, signed by Hungary’s president this week, persons with loans denominated in Swiss francs can pay them off using an exchange rate of 180 Hungarian forints to the franc — about a 25 percent discount to the current market rate of almost 240 forints. There are similar bargains offered on loans denominated in euros and Japanese yen.

It is not clear how much this will really help homeowners. Few of them have the money on hand to pay back their loans, and to get the money they presumably would have to borrow from banks. Andras Simor, the governor of Hungary’s central bank, estimates that only one-fifth of borrowers will be able to take part.

The move has outraged the financial establishment of Europe. It represents a serious breach to the patterns followed in much of the world since the financial crisis burst open three years ago. Banks have lost a lot of money, and been bailed out, but bank executives have done quite well. Those who lent money to banks have generally gotten all their money back. Customers by and large have been forced to bear the brunt of their behavior, whether or not there was evidence the banks had misled them.

In Hungary, the lure of foreign currency loans back in 2005 was clear. Interest rates on mortgages denominated in Swiss francs were around 4 percent, while rates on forint loans could be in the double digits. Thanks to the lower monthly payments, a buyer could qualify for a Swiss franc loan who could not hope to get a loan in local currency. Soon a vast majority of mortgage loans were made in Swiss francs.

The risk was obvious. All the borrowers had income in forints, not francs. If the forint lost value, their loan payments could multiply.

Now the government claims that banks misled borrowers. The extent to which that is true is hard to gauge. But there is no doubt that a widely voiced theory was that because Hungary was a growing economy, its currency should appreciate against the staid old currencies of Western Europe. And that is exactly what happened in the years running up to the credit crisis. Those who failed to take out mortgages in Swiss francs or euros looked foolish.

When the forint began to lose value, banks did try to ameliorate the situation. In 2009, they offered to extend loan periods, so that homeowners could make lower monthly payments that would last for more years.

Earlier this year, with the forint around 220 to the franc, the banks came up with a plan that was reminiscent of the pay-option loans that helped to create the American financial mess. Borrowers could choose to make payments as if the forint were at 180 to the franc, and continue to do that through 2014. That would leave many with manageable payments, since most of the loans were taken out at exchange rates from 140 to 180 forints to the franc.

The savings from those lower payments would, however, simply be added to the principal of the loan. It was negative amortization, likely to postpone the pain but not alleviate it.

Floyd Norris comments on finance and the economy at nytimes.com/economix.

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