It was in 1950 that Jacques Rueff, one of France's most influential liberal thinkers and economists of the 20th century, declared: "Europe will become united through its money or not at all."

That this prophecy is about to be put to the test, with the introduction of euro banknotes and coins from January 1, is in no small measure due to the hard work of the European Central Bank.

"The euro is much more than just a currency," Wim Duisenberg, the ECB president, says. "It is a symbol of European integration in every sense of the word."

Few dispute the skill with which the ECB has mastered the technical challenge of introducing the euro, both as a "virtual" currency in 1999 and now in the form of banknotes and coins. But there are wider misgivings about its management of monetary policy - the timing of its policy decisions, its methods of operation and its official strategy.

The question is whether its shortcomings have been just the teething problems of an infant institution obliged to take instant charge of a global currency, or symptoms of enduring structural weakness.

Criticism of the ECB's steering of interest rates tends to focus on the suggestion that it sometimes reacts too slowly to changing economic conditions. Barry Eichengreen, economics professor at the University of California at Berkeley, says he has "a slight fear that the ECB looks at the world through a rear-view mirror".

In particular, the ECB has been faulted this year for underestimating the impact of the US recession on the eurozone and for waiting too long before cutting interest rates. In their defence, ECB officials say experts on both sides of the Atlantic were inclined at the start of 2001 to think that the eurozone would be shielded to a considerable extent from the US downturn.

They also reject as simplistic the notion that the ECB should have cut interest rates as aggressively as the US Federal Reserve. "The way monetary policy is transmitted in the US, and the structure of the US financial system, are very different from in the eurozone. Here, banks are more important. In the US, it's the markets. That justifies US monetary policy being more responsive to the markets," one official says.

"Over time, the Fed tends to increase interest rates a lot, and then cut a lot. It will never happen that way in Europe."

However, when the ECB eventually cut rates last May, it did so after a period of unusual confusion between the bank and the markets. The bank had appeared to signal in April that a cut was imminent, but did not act. It then switched track in May by cutting rates after suggesting they would be kept on hold.

Part of the problem stems from the ECB's eagerness to communicate openly with markets and the general public. The bank is sometimes accused of secretiveness, because it does not publish minutes of its meetings, but in some respects it says too much in public.

The most damaging example was in October 2000, when Mr Duisenberg broke an unwritten rule among central bankers by talking in a newspaper interview about whether the ECB might intervene on currency markets in support of the euro.

Other members of the bank's policymaking Governing Council give frequent speeches and interviews. Mr Duisenberg holds a news conference once a month after monetary policy meetings, and testifies on a regular basis to the European Parliament. The ECB also publishes a detailed monthly bulletin, with economic forecasts twice a year.

A careful re-reading of past bulletins, and of the prepared statements with which Mr Duisenberg has started his news conferences, indicates that these have usually been the two most authoritative guides to the ECB's future monetary policy actions. Both reflect the influence of Otmar Issing, the ECB's chief economist, who also makes a recommendation on interest rates to the council before each monetary policy meeting.

But this leaves a question mark over what weight to place on the public remarks of Mr Duisenberg and his colleagues. With Alan Greenspan, the Fed chairman, it is assumed that his views are decisive for Fed policy.

This is not necessarily the case with Mr Duisenberg. In a reflection of the way business is conducted in many European Union institutions, he strives to build a consensus among the ECB council members.

Julian Callow, economist at Credit Suisse First Boston, says the desire for consensus partly reflects the ECB's multi-national character. "The formation of the ECB has involved a tremendous concentration of power, from 12 national central banks to effectively one organisation," he says.

"Many senior central banking officials, especially national governors, had been accustomed to a highly visible public profile, and inevitably still want their voices heard in public and private."

Outside the eurozone, some central bankers say the ECB's teething difficulties may reflect the fact that, before the euro's launch, many European central banks lacked experience in running independent monetary policies. Moving in line with the Bundesbank was the order of the day for many of them.

The Bundesbank's legacy is visible in the ECB's official strategy. In recognition of the German central bank's unequalled anti-inflationary record, the ECB set itself the primary objective of keeping inflation below 2 per cent a year.

To achieve this goal, the ECB adopted a "two-pillar" strategy. The first pillar involves a close monitoring of M3 money supply growth, and the second an assessment of the inflation outlook based on indicators such as economic growth, the exchange rate, fiscal policy and business and consumer surveys.

Even some ECB council members now appear uncertain about the value of M3 as an accurate guide to inflation trends. "I would say that while it must be clear that the ECB is not planning to abandon M3, I personally cannot rule out that some day M3 could abandon us," says Guy Quaden, Belgium's central bank governor.

Thornier still is the question of whether the 2 per cent inflation target is too restrictive. Given that many eurozone countries have been historically prone to high inflation, the ECB's determination to build a reputation for guaranteeing price stability is understandable.

But the 2 per cent ceiling is so low that it can easily be overshot, as it was in 2000 and this year, because of unexpected shocks such as rising food and oil prices that do not necessarily threaten medium-term price stability.

Guido Tabellini, economics professor at Milan's Bocconi University, is among those experts who say a wider inflation target of 1 to 3 per cent would offer the ECB more room for manoeuvre on interest rates.

Mr Issing and his ECB colleagues never tire of pointing out that low inflation is the best contribution the ECB can make to economic growth. Moreover, some responsibility for improving the eurozone's growth performance clearly rests with national governments, many of which are only slowly deregulating labour and product markets and easing tax burdens on employment.

In this sense, much criticism of the ECB is aimed at the wrong target, they say. Powerful though it is, the ECB is only one actor among many in the eurozone. It will require a bigger effort by all to raise growth, sharpen competitiveness and make a long-term success of the euro.