Other parties to the case making arguments on Tuesday that were broadly supportive of the central bank were lawyers from some member states of the European Union including Ireland, Italy, Poland and Spain.

A lawyer representing the German government addressed the court with a comparatively cautious argument in favor of the central bank’s bond-buying policy. “The E.C.B. does have wide discretion,” the lawyer, Ulrich Häde, told the court. “But in using this, it must stay within the bounds of its mandate and the prohibition of monetary public finance.”

The mere threat of intervention by the European Central Bank was enough to tame financial markets, and the bank never had to buy any bonds as part of that program. But the legality of bond buying by the central bank remains an issue because of expectations it will soon buy large quantities of government bonds to stimulate the flailing eurozone economy.

Analysts do not expect the Court of Justice to place severe restrictions on the central bank’s bond buying. But if the judges did so, the central bank could be deprived of a tool seen as essential to holding off the specter of deflation — a broad decline in prices that can undercut company profits and overall employment and growth. At 0.3 percent, the inflation rate in the eurozone is already worrisomely low, and well below the target of about 2 percent that the European Central Bank considers optimal for growth and financial stability.

The suit, brought by a group of university professors as well as about 30,000 citizens who oppose using German funds to prop up the euro, was initially heard by the German constitutional court, which referred it to the Court of Justice of the European Union. In a decision that many legal experts criticized as muddled, the German high court reserved the right to block German participation in any bond buying by the European Central Bank, even if the Court of Justice has no objections to the central bank’s plan.

There has been a surge of discontent in Germany toward policies of the European Central Bank. In recent state elections, an anti-euro party, the Alternative for Germany, has been siphoning votes from Chancellor Angela Merkel’s Christian Democrats.

Many Germans fear that they would wind up paying if the European Central Bank buys government bonds from eurozone countries that later default. The central bank has already announced its intention to begin large-scale purchases of private-sector securities, and many analysts expect purchases of government bonds to begin next year.