"We welcome the launch of the euro, an historic step that 11 nations in Europe have taken toward a more complete Economic and Monetary Union," Clinton said in a statement. "A successful economic union that contributes to a dynamic Europe is clearly in our long-term interests."

"A strong and stable Europe, with open markets and robust growth, is good for America and for the world," he added.

Clinton's endorsement of the euro, which on Monday made a strong debut on the world's foreign exchange markets, followed a series of more guarded comments by other top US officials.

Treasury Secretary Robert Rubin earlier repeated his long-standing mantra that what is good for Europe will be good for the United States -- adding, that the euro's launch underscored the need for sound economic policies at home.

"It will be a currency like all other currencies," he told reporters. "As we've said many times, if it's good for Europe then that's good for the United States. A strong Europe is good for the United States."

The 11 countries that adopted the single currency -- Austria, Belgium, Finland, France, Germany, Ireland, Italy, Luxembourg, the Netherlands, Portugal and Spain -- almost match the United States' economic might.

Their total annual output of about $6.5 billion compares to almost $8 billion in the United States. And according to European estimates, the euro zone will form the world's greatest trading power, with 1997 exports 25 per cent larger than those of the United States and twice those of Japan.

The euro zone's weight in the world economy has prompted some to fear a shift of investor money out of the US dollar into the euro. That would make it harder for the United States to attract the capital it needs to finance its rising trade deficit, push up interest rates and put a damper on growth.

But analysts say that the new European central bank will need some time to prove its mettle.

"I think (the euro) could become a competitor to the dollar in the sense of looking for a safe haven in an uncertain world, but that would be some time down the road and there's bound to be a certain amount of uncertainty connected with the euro," former Federal Reserve chairman Paul Volcker told Reuters Television.

Former Fed governor Lawrence Lindsey concurred: "I think that is not an issue in the short run. At the start, the euro is going to have problems as a reserve currency. It will ... have to earn its place."

Rubin and his deputy Lawrence Summers said the dollar's future would depend crucially on the pursuit of sound, growth-oriented economic policies in the United States.

"I think ... the euro just reemphasizes how important it is that we focus on our own policies, and continuing to make the United States a place where people want to invest their capital by having sound policies here -- particularly by maintaining our fiscal discipline," Rubin said.

And Summers added: "As far as the dollar is concerned, the buck stops here. As long as we keep our fundamentals strong, I think the dollar (and) US borrowing costs will do just fine."

Washington's cautious approach to the euro reflects US concerns that Europe might turn its back on problems elsewhere in the world economy as it concentrates on making its unprecedented currency union work.

At the same time, US officials have warned repeatedly the focus on the euro must not deflect from structural reforms to reduce sky-high unemployment rates in much of Europe.