After his appeal to Americans this week for renewed support of U.S. goals in Iraq, President Bush is dispatching a new ambassador to Baghdad to exercise more assertive diplomacy, which will include a wider reaching-out to opposition groups and attempts to accelerate Iraq's progress toward military self-reliance.

Zalmay Khalilzad is charged with overseeing the last and most sensitive period of the political transition, as Iraqis scramble to meet the deadline for a new constitution -- now just six weeks away without a single word written -- and then hold elections for a permanent government. His mission is to avoid any slippage in the schedule.

The Afghan-born diplomat said he intends to bring the kind of aggressive engagement that typified his recent stint in Kabul, where he was known to nudge, cajole, prod and occasionally demand rival groups make compromises or make the Afghan government move on tough decisions.

"My personal idiosyncrasies are that I'm proactive and I engage people," he said in an interview this week in Washington as he prepared to leave for Baghdad. "I also believe strongly in balance. If you rely too much on the military, then the hammer is the only instrument you have and everything then looks like a nail. I believe in the minimum use of force, which means bringing people together to see if they can find a nonviolent way to solve problems."

The key, he said, is to make sure Iraqis who join the political process "don't lose face, which is so important in that part of the world, to make them feel as they back down that there is an honorable path for them."

Khalilzad, affectionately called a "gadfly diplomat" by a senior State Department colleague, also represents a change in the visibility of U.S. diplomacy in Baghdad. During the first phase after the ouster of Saddam Hussein, U.S. administrator L. Paul Bremer basically ruled Iraq for 14 months. He was followed during the second phase by Ambassador John D. Negroponte, who deliberately moved into the shadows to show that the U.S. role had shifted from postwar overseer to envoy to a sovereign state, State Department officials say.

A senior State Department official involved in Iraq policy said Khalilzad's role will be to "unhitch snags, keep the focus on the big picture and steady nerves."

In a speech Tuesday night, Bush appealed to the American public not to lose faith in the ongoing U.S. effort, even as recent polls have shown a wavering of public support for the Iraq policy. The president focused on strides Iraq already has made toward establishing a democratic government, and urged the public not to lose "our heart, our nerve" during "a time of testing."

The strong U.S. hand in Iraq of the past is likely to be felt again as the country makes its way through the third phase of the transition, with the U.S.-orchestrated Transitional Administrative Law providing the framework for a new constitution, U.S. officials say. One big issue is the role of Islam. Another is how Iraq's diverse ethnic and religious communities come under one umbrella in a federal state with regional powers.

Many U.S. officials say they hope the transitional law prevails as a major part of the new constitution, particularly on two points: first, that Islam is a source of law but not the only source of law; and second, that Iraq continues the federal arrangement that allows local groups to keep their identity but share national resources and policy goals, somewhat like Belgium or Switzerland. The role of Islam is particularly important to Iraq's Shiite majority as well as to Islamic parties, while the issue of federalism is key to support from the Kurds who want to retain some autonomy in northern Kurdistan.

Khalilzad, who was educated at the American University in Beirut and the University of Chicago, also intends to press for rapidly expanding Iraq's role in security. "We would like to see how to accelerate Iraq's self-reliance" while also making sure that forces are "capable and trusted so that they are not the instrument of one group and have the confidence of all," he said.

On his visit to the United States last week, new Prime Minister Ibrahim Jafari said his main message to the Bush administration is to expedite the political transition.

In Baghdad, Iraqis are counting on Khalilzad to help galvanize Iraq's political process, which was seriously deferred when the winners in January elections then took three months to form a government, eating up time that was supposed to be spent on the constitution. While at the National Security Council, Khalilzad helped bring Iraqis together before and after the 2003 U.S. invasion of Iraq.

"He's not new to the scene, and he does come with relevant experience" earlier in Iraq and Afghanistan, said Laith Kubba, spokesman for Jafari. "All in all, he speaks Farsi, he speaks some Arabic, he is a Muslim -- all that makes a difference. He's going to deal with many persons he has met with before. . . . He knows Iraqis."

Khalilzad is also seen in Baghdad as having particular sway in Washington after serving as America's top diplomat in Afghanistan after the ouster of the Taliban. "He might be useful to Iraqis, in the sense he is close to the administration," said Subhi Nadhim Tawfiq, professor of political science at the University of Baghdad 's Center for International Studies. "Surely he is going to play an active role . . . in pushing the political process."

But with the timetable for a constitution just six weeks away, Khalilzad said the assignment will be the "toughest mission of my life. Time is short, and there's a lot to be done," he said. "I'm optimistic . . . but someone also suggested that I should have my head checked."

Mosher reported from Baghdad. Special correspondent Khalid Alsaffar contributed to this report.

Zalmay Khalilzad has experience in the region, having served as the top U.S. diplomat in Afghanistan after the fall of the Taliban.