A Democratic field of candidates sobered by a recent racial feud is returning carefully to direct conflict, with Senators Clinton and Obama arguing over the role of the president while agreeing to confront together the current commander in chief on his war powers.

At a debate last night in Las Vegas, Mrs. Clinton asked Mr. Obama to join her in sponsoring Senate legislation that would force President Bush to seek congressional approval for any future agreements with the Iraqi government.

“We have to do everything we can to prevent President Bush from binding the hands of the next president,” Mrs. Clinton said, using a new format allowing the candidates to ask a direct question of each other.

Seated a few feet away from the former first lady, Mr. Obama seemed to have little choice but to say yes. “I think we can work on this, Hillary,” he replied.

The move by Mrs. Clinton signaled a bid to mute Mr. Obama’s edge with anti-war Democrats familiar with his opposition to the invasion of Iraq, but it also exemplified the more collegial tone of last night’s debate.

The two-hour event took place on the heels of a bitter back-and-forth among the campaigns on the issue of race, which began when Mrs. Clinton last week touted the leadership of President Johnson in enacting the landmark Civil Rights Act of 1964, a comment that some African American supporters of Mr. Obama took as a slight to the Reverend Martin Luther King Jr. The dispute escalated until Monday night, when both Mr. Obama and Mrs. Clinton called a truce, praising each other’s record on civil rights and appealing for party unity.

With the Nevada caucuses set for Saturday, MSNBC moderators Brian Williams and Tim Russert began the questioning on that issue, and each candidate took pains to avoid rekindling the racial tension. “I think what’s most important is that Senator Obama and I agree completely that, you know, neither race nor gender should be a part of this campaign,” Mrs. Clinton said, adding that each campaign had “exuberant and sometimes uncontrollable supporters” who occasionally crossed the line.

Mr. Obama and the third candidate on the stage, John Edwards, echoed the sentiment. “I think Hillary said it well,” Mr. Obama said.

The candidates did draw contrasts with each other — albeit politely — on a few issues. Mrs. Clinton criticized Mr. Obama for supporting what she called the “Dick Cheney-lobbyist energy bill” in 2005, which she said was a “big step backward” for America, and she took aim at Mr. Edwards for changing his position on the nuclear waste repository at Yucca Mountain, a key issue in Nevada. Mrs. Clinton also belittled what Mr. Obama described as his approach to the job of president. Expanding on his comments to a Nevada newspaper that he would not be an “operating officer,” he said a president should focus on offering a broad vision for the country instead of just “making sure that schedules are being run properly or the paperwork is being shuffled effectively.”

“I respect what Barack said about setting the vision, setting the tone, bringing people together,” she said. “But I think you have to be able to manage and run the bureaucracy. You’ve got to pick good people, certainly, but you have to hold them accountable every single day.”

“We’ve seen the results of a president who, frankly, failed at that,” she added, citing the Bush administration’s response to Hurricane Katrina. Mr. Obama replied that “there’s no doubt you’ve got to be a good manager.”

He later offered his own Bush comparison for Mrs. Clinton, accusing her of following what he characterized as the current administration’s fear-based political playbook by talking up the threat of terrorism as the elections in Iowa and New Hampshire drew near earlier this month.

For all the lingering acrimony over race this week, perhaps the biggest question in the hours before the debate was whether a long-shot hopeful, Rep. Dennis Kucinich, would be allowed to participate. The Ohio congressman had sued NBC Universal after MSNBC rescinded its invitation following his distant finishes in Iowa and New Hampshire earlier this month.

A Nevada district judge had ruled in Mr. Kucinich’s favor on Monday, but after the network appealed, the state’s seven-member Supreme Court overturned the decision just an hour before the debate 9 p.m. scheduled start time last night. Mr. Kucinich was kept off the stage.

The latest poll from the Reno Gazette-Journal released this week shows a tight three-way race in Nevada, with Mr. Obama edging Mrs. Clinton by 32% to 30% and Mr. Edwards not far behind, at 27%. The margin of error was plus or minus 4.5 percentage points, making for a statistical dead heat.