FRANKFURT — Worried that Europe’s debt impasse posed a growing threat to the global financial system, the world’s major central banks moved Thursday to assure that European banks would not run short of cash as troubled nations like Greece and Italy sought to stabilize their economies.

The central banks, in a coordinated action intended to restore market confidence, agreed to pump United States dollars into the European banking system in the first such show of force in more than a year. Some banks have found it hard to borrow dollars as American lenders grew nervous about their financial condition.

Thursday’s action, coming almost exactly three years after the collapse of the investment bank Lehman Brothers, lifted global stock markets, sharply increasing the value of shares in banks heavily exposed to debt from Greece and the other struggling members of the euro zone. The euro, which had been falling in recent days, rebounded.

The central bank action came as European finance ministers and other policy makers were gathering in Wroclaw, Poland, for meetings on Friday and Saturday. The United States Treasury secretary, Timothy F. Geithner, who was scheduled to attend, was expected to urge European officials to act more aggressively to contain the sovereign debt crisis, which has already begun to undercut growth in Europe.