Washington - For US President Bush, it's not a question of whether he will veto a congressional measure calling for withdrawing troops from Iraq, but rather when he will do it.

Special coverage: War in Iraq Related readings: Leader of Al-Qaida in Iraq killed Democrats woo voters with Bush attacks US announces 9 troop deaths in Iraq Bush warns Congress over Iraq timetables US Congress passes Iraq pullout bill US Democrats authorize subpoena for Rice

Democratic congressional aides said they anticipate that Bush will reject the Iraq funding bill Wednesday after receiving it from Capitol Hill on Tuesday. That would force the democratically controlled Congress to revisit the dilemma of how to give troops in the field the money they need while satisfying opponents of the war who want US involvement ended.

Bush on Monday repeated his intention to veto the US$124.2 billion measure, citing the withdrawal language as well as funding for nonmilitary projects. Although he said he wanted to work with Democrats, he made clear he wasn't giving in on the question of setting a timetable for withdrawal.

"I'm optimistic we can get something done in a positive way," Bush said.

US Senate Majority Leader Harry Reid, who said the bill would arrive at the White House on Tuesday, urged the president to reconsider his veto promise.

"If the president wonders why the American people have lost patience, it is because the news out of Iraq grows worse by the day," Reid said.

The funding bill would require troops to begin leaving Iraq in October, a provision Democrats see as meeting the mandate they received from voters in the November elections that gave them control of Congress. Bush has argued that setting a firm date for withdrawal would be counterproductive because it would embolden terrorists and others creating havoc in Iraq.