Gen. David H. Petraeus’s decision to withdraw another combat brigade six weeks ahead of schedule reinforced the assurances by Iraq’s defense minister that his troops could handle more of Iraq’s security and sent a signal that the American troop withdrawals would become a reality.

An Obama administration is also expected to shift the focus to Afghanistan. American officials have said that as the war deteriorates in Afghanistan, any additional forces sent there would have to be from among troops withdrawn from Iraq.

Mr. Obama’s election also coincided with the American negotiators’ acceptance of many of the changes Iraqis demanded in the agreement, which created an overall picture that was easier both for the Iraqis and their neighbors  Iran, Syria and Saudi Arabia  to accept.

The American negotiators sent a new version of the agreement to Iraqi leaders on Thursday that included many of the changes Iraqis had demanded. In public, Iraqis said merely that they were studying the document.

Over all, however, there was a new tone of optimism. “The atmosphere is positive with the American attempt to preserve the sovereignty of the Iraqi nation,” the government’s spokesman, Ali al-Dabbagh, told the news channel Al Arabiya. He praised the inclusion of a new provision stating that Americans would not launch attacks on Iraq’s neighbors from Iraqi soil.

The Americans also added language to make explicit what kinds of troops would remain after the withdrawal in 2011, said a Bush administration official knowledgeable about the security pact. Those still in Iraq would be primarily trainers and air traffic controllers, the official said.

“There’s going to be a significant presence, but they are not going to be ‘combat’ forces,” said the administration official. The official said that the most recent talks with Iraqis had given American negotiators confidence that a final agreement was close.