During his visit to the NATO headquarters in Brussels, Zebari warned that the "consequences of failure" in Iraq could resonate well beyond the country's borders.
"That's why the stakes are high. That's why we need the contributions and help of many countries," he said, speaking to ambassadors from the military alliance's 26 members.
"It isn't just a question of numbers for our forces but also the quality of leadership and the possibility for our forces to be self-reliant," he said. "These coming months are very critical for the success of this process in Iraq."
He said that Iraqi authorities were aiming to draft a constitution by Aug. 15, which would be submitted to voters in a referendum in October, with new general elections to follow at the end of December.
Earlier Zebari held talks with NATO Secretary General Jaap de Hoop Scheffer.
NATO is making preparations to open a military "academy" near Baghdad to train high-level officers.
Zebari was speaking on the eve of a conference here, bringing together more than 80 foreign ministers and officials to show solidarity with the war-torn nation, and to hear Baghdad's plans for the rebuilding of the country.
Iraq has sent a 30-member delegation that includes Zebari, Prime Minister Ibrahim Jaafari, as well as the defense, interior, finance and justice ministers and independent experts.
UN Secretary General Kofi Annan was to join ministers including US Secretary of State Condoleezza Rice, as well as foreign ministers from Iraq's neighbors including notably Iran and Syria, the G8, China, NATO and the Arab League.
The conference is co-hosted by the European Union (EU) and the United States, whose ties were deeply strained by the 2003 Iraq war.
US President George W. Bush hailed the fact that the EU was co- hosting the talks when he met EU leaders in Washington Monday.
"It's an important signal for people to hear loud and clear, that there may have been past differences over Iraq, but as we move forward there is a need for the world to work together," he said at the White House.
"The international consensus that has long eluded us on Iraq is now in place," said EU foreign policy chief Javier Solana ahead of the two-day international conference, starting Tuesday evening.