The three top contenders for the U.S. presidency laid out their very different views on the Iraq war during testimony by two top officials on Tuesday.

Democratic hopeful Sen. Hillary Clinton told a Senate Armed Forces Committee hearing Tuesday that she thinks "it's time to begin an orderly process of withdrawing our troops, start rebuilding our military, and focusing on the challenges posed by Afghanistan, the global terrorist groups and other problems that confront America."

In his opening statement, presumptive Republican nominee Sen. John McCain said: "I do not want to keep our troops in Iraq a minute longer than necessary to secure our interest there.

"Our goal, my goal, is an Iraq that no longer needs American troops. And I believe we can achieve that goal, perhaps sooner than many imagine. But I also believe that the promise of withdrawal of our forces, regardless of the consequences, would constitute a failure of political and moral leadership."

Sen. Barack Obama, the other Democratic presidential hopeful, had his chance to address Gen. David Petraeus and Ambassador Ryan Crocker later in the day when they appeared before the Senate Foreign Relations Committee.

He advocated a very different approach, saying the status quo isn't working and the U.S. should consider sitting down with neighbours like Iran to discuss the options.

"I do not believe we are going to be able to stabilize the situation without that," Obama said, referring to what he called a "diplomatic surge that includes Iran."

He also said a firm timetable for U.S. troop withdrawal would force the Iraqi parliament to meet the challenge of self-governance.

"I think that increased pressure in a measured way, in my mind, and this is where we disagree, includes a timetable for withdrawal. Nobody is asking for a precipitous withdrawal."

CTV's Joy Malbon said that position separates Obama from the others.

"Sitting down with the enemy is not received very lightly here but Senator Obama has talked about that before saying 'look, we have to be diplomatic here, you can't just go invading countries. We've got two wars on the go.' He has always advocated that," Malbon told CTV Newsnet.

She said there was none of the usual campaign-style crossfire between Obama and Clinton on Tuesday, and all the candidates appeared anxious to appear presidential.

"It was about getting their campaign voice out there and certainly appealing to voters," Malbon said. "Not a lot of people are watching these hearings all day I can tell you that, but the clips will be played over and over again."

At the morning hearing, Petraeus, the U.S.'s top general in Iraq said the surge has suppressed violence there, even though progress is uneven, and ongoing U.S. troop withdrawals should continue until July.

However, Petraeus said Tuesday that while troop levels can be drawn down to the pre-surge level by then, he wants any further withdrawals suspended for 45 days to evaluate the situation, followed by an indeterminate assessment period.

That would leave an estimated 140,000 U.S. troops in Iraq. In early 2007, U.S. President George Bush ordered an increase in U.S. troop levels in Iraq, raising it to more than 160,000. Last fall, Bush said a gradual draw-down of troops would take place.

Petraeus said while security has improved in Iraq since his report last September, the situation remains fragile and reversible.

While committee chairman Sen. Carl Levin questioned Petraeus, a spectator started chanting "bring them home!" -- referring to U.S. soldiers in Iraq. Security personnel removed the man from the room.

Petraeus couldn't give Levin an estimate of how many troops would be left in Iraq by year's end, assuming everything went well.

Clinton told Petraeus that the original purpose of the surge was to give Iraqis the "space" to make political progress towards national reconciliation.

This reconciliation doesn't appear to be happening, she said, adding this ongoing heavy presence in Iraq has real costs in a variety of areas that the war's supporters downplay.

"What conditions would have to exist for you to recommend to the president that the current strategy is not working?" she asked Petraeus.

The general said there's been progress, but not satisfactory progress, in a number of areas.

Al-Sadr

While U.S. officials tout the surge's success, there has been significant conflict in Iraq in recent days, mainly between Iraqi government forces and Shiite militants loyal to radical cleric Muqtada al-Sadr.

Aides to al-Sadr said the cleric is calling off a mass rally planned for Wednesday in Baghdad. The event was to mark the fifth anniversary of the city's fall to U.S. forces after the March 19, 2003 invasion.

However, some observers thought the "million-strong" march was really intended to be a show of strength as part of al-Sadr's confrontation with the U.S. and Iraqi governments.

Al-Sadr's militia has observed a seven-month ceasefire -- and many have said that the ceasefire has helped bring down violence levels in Iraq.

Last week, the ceasefire buckled as fighters loyal to al-Sadr battled Iraqi troops in Baghdad and Basra in far southern Iraq.

U.S. and Iraqi troops have been stepping up military pressure on Sadr's fighters in their Sadr City stronghold -- a Shiite slum within Baghdad.

Al-Sadr has threatened to call off the ceasefire if the Iraqi government failed to protect people from "booby traps and American militias." He wants a timetable for American forces to be out of Iraq.

McCain questioned Petraeus about the Basra situation, where more than 1,000 Iraqi security forces deserted or under-performed during recent fighting with Shiite militia members.

Petraeus said local Iraqi police still have difficulty working in areas where there is heavy intimidation, but added the Iraqi forces have improved their performance in recent days.

"Taken as a snapshot, with scenes of increasing violence, and masked gunmen in the streets, it is hard to see how this situation supports a narrative of progress in Iraq,'' Crocker said.

"There is still very much to be done to bring full government control to the streets of Basra and eliminate entrenched extremist, criminal, and militia groups. When viewed with a broader lens, the Iraqi decision to combat these groups in Basra has major significance.''

With files from The Associated Press