PARIS — The European Central Bank announced Wednesday that it is loaning about $640 billion to European banks for an unusual three-year term as part of its effort to free up credit tightened by the euro zone’s government debt crisis.

Statistics released by the Frankfurt-based ECB showed that 523 banks signed up for the loans, the largest infusion of cash since the euro became the common currency of a number of European nations in 1999. In all, 17 nations have adopted the currency, which was seen at its inception as a boost to economic stability but has in recent months come under withering and perhaps fatal attack.

The currency has suffered because a number of European governments — Greece being the most acute example, but also Italy and Spain — have rolled up debts so high they are finding it difficult to reimburse what they owe on schedule.

The ECB’s willingness to make such a large amount of money available, at only 1 percent interest, reflected its concern that banks must be able to pay off their own debts and, eventually, increase the amount they loan to businesses. That, economists say, is a prerequisite for European economies to resume healthy growth in 2012.

Howard Archer, chief European economist at IHS Global Insight in London, said the loans “will go a long way” toward helping European banks make credit available to businesses in need. Tight credit has been cited as a major reason for the economic slowdown that has gripped most of Western Europe.

Restoring growth in European economies would mean not only less austerity for citizens but also more tax revenue for governments and the opportunity to reduce their large deficits and similarly large public debts.

Reports in Paris suggested some governments also hope the loans will make it possible for banks to buy government debts when cash-strapped governments issue bonds early in 2012. In effect, the reports said, this would be an indirect way of having the ECB become the lender of last resort for indebted governments — something it is forbidden from doing directly by its founding statutes.

“This is not the end of the crisis, but it is an enormous relief for next year’s refinancing.” Jean-Francois Robin, an analyst at the Natixis bank, told the newspaper Le Monde.

Archer, the London analyst, said some banks are likely to use their improved positions to buy government bond issues, but probably in safer countries rather than heavily indebted Greece, Italy, Portugal or Ireland.

“There is a profit to be made borrowing at 1 percent and buying sovereign debt with yields a lot higher,” he said.

France, in particular, is hoping for loans from its banks, according to the assessments in Paris. The French government has calculated that it will have to raise more than $230 billion in 2012 to pay off due loans and service its remaining debt.

Other countries will need even more. Germany will have to raise more than $240 billion, and Italy will need to borrow $300 billion. In all, euro-zone countries will be seeking well over a trillion dollars from banks and other financial institutions, according to estimates by French economists that were published in Paris.

Seeking another source of funding, European governments on Monday pledged to transfer $195 billion to the International Monetary Fund in hopes that the financial institution will in turn make loans to needy European governments and, in the process, impose budget-tightening conditions that the European Union itself would be unable to enforce.

The idea was that other, non-European nations would also make funds available to the IMF to help rescue staggering European governments. That would spread the risk beyond the 17 euro-zone nations, in addition to raising the total available as Italy and other debt-heavy countries go to the market in the months ahead.