The United States is the largest shareholder in the International Monetary Fund and has played a forceful, interventionist role in financial crises since the early 1990s, in countries like Mexico, South Korea, Russia and Argentina. But as Europe gropes for a solution to a debt crisis that threatens to spread from Greece to Portugal and Spain, American officials have been resolutely low-profile. 'There's a sense in the Obama administration that it's Europe's responsibility to straighten out problems in the euro zone,' said Randall W. Stone, a political scientist at the University of Rochester and an authority on the IMF. 'I suspect that any kind of overt interference wouldn't be appreciated very much.' American involvement has so far been behind the scenes. Treasury Secretary Timothy F. Geithner discussed the crisis last Friday with other finance ministers from the Group of 20 nations, and again on Sunday with the Greek finance minister, George Papaconstantinou, who was here for the IMF spring meetings. President Barack Obama spoke with the German chancellor, Angela Merkel, by phone on Wednesday. But in public, American officials have said little beyond bland statements of support for the IMF and the European Union. 'This is clearly a European issue and we think that it's important that the European leaders and the European structures be centrally involved in the management of the problem and the resolution of the problem,' said an administration official, who spoke on condition of anonymity because of the sensitivity of the matter. 'However, it is also clear that the IMF is now a central part of the solution.' The official added: 'We're following these things very closely, thinking through different alternatives of what can be done and what should be done with our counterparts in Greece and the EU.' Stone said the silence was not just substantive, but strategic as well. Jittery bond dealers have so much leverage over the situation right now that any perception of United States pressure on the IMF could throw the already complicated situation into an unpredictable tailspin, he said. 'It's very much up in the air whether the current package can stem the run on the Greek bond market,' Stone said. 'From a psychological point of view, the Europeans want to convince the market that adequate steps have been taken so that investors can come back in. The most supportive the administration can be for the IMF right now is to be quiet.' 