WASHINGTON - In another sign of U.S. determination to move on Iraq, the Bush administration said on Thursday it was amassing evidence of war crimes by Saddam Hussein and left open the possibility it might back a tribunal to bring him to account. 

Although the administration is vehemently opposed to a permanent international criminal court and has called for the end of two ad hoc tribunals dealing with war crimes and genocide in Rwanda and Yugoslavia by 2008, it has not ruled out future ad hoc tribunals. 

The U.S. ambassador at large for war crimes, Pierre-Richard Prosper, told Congress he has two assistants assigned to investigate Iraq and they are working on a ``daily basis'' to develop data on atrocities blamed on Saddam and top aides. 

``We do believe that Saddam Hussein and his top lieutenants need to be held answerable for their actions. ... We have taken steps to collect information regarding abuses that have occurred. ... It is an effort that my office is involved in on a daily basis,'' he told the House of Representatives Committee on International Relations. 

Rep. Tom Lantos, a Democrat from California, raised the issue of a possible international war crimes tribunal for Iraq, citing Saddam's programs to develop weapons of mass destruction and charges that he gassed Iraqi Kurds in the village of Halabja in 1988. 

Prosper said he did not know what jurisdiction might ultimately prosecute Saddam. If the Iraqi leader is ousted from power, as Washington wants, an Iraqi judicial institution might be able to do the job but in any event, ``we do believe there needs to be a forum created to address this issue,'' he said. 

``What I'm saying is that we will definitely be looking for some sort of mechanism to create this and I think it is difficult at this time to state precisely what that mechanism might be,'' he said. 

The administration has increasingly focused on effecting ''regime change'' in Iraq as part of its post-Sept 11 anti-terrorism war. 

Prosper made his comments during a hearing in which he criticized the Hague tribunals prosecuting war crimes and genocide in Rwanda and Yugoslavia and urged that their work end by 2008. 

He also reinforced vehement Bush administration opposition to a proposed International Criminal Court that would be a permanent structure for prosecuting war crimes and genocide. 

The administration fears that the permanent court would impinge on U.S. sovereignty by subjecting American military forces to prosecution at a time when they are increasingly deployed around the world in the war against terrorism.