The top U.S. commander in Iraq presents a long-awaited progress report to Congress on Tuesday but will offer little hope for improved security before a new American president takes over in January.

All three contenders for the U.S. presidency will be among the senators questioning Gen. David Petraeus, who is expected to say he will interrupt a series of troop withdrawals in July to evaluate security conditions.

That decision, made as rising violence threatens to unwind gains made last year, could leave more than 130,000 U.S. troops in Iraq though to the end of President George W. Bush's term.

In testimony over two days, Petraeus and U.S. Ambassador to Iraq Ryan Crocker will assess the uneven progress made in a year-long "surge" of force meant to create the calm for Iraqi politicians to advance legislation and factions to reconcile.

The upturn in violence has thrust Iraq back to the forefront of campaigns for the November presidential election.

Leading Democrats have already criticized Petraeus' plan to halt withdrawals. They say the surge has failed to yield political progress and that the Bush administration has found no way to end U.S. involvement in the conflict.

"The president's plan is to muddle through and hand the problem to the next president," said Sen. Joseph Biden, a Delaware Democrat and chairman of the Senate's Foreign Relations Committee.

"I don't think they know what to do. I see no evidence of a political plan," he said.

All three presidential contenders - Republican John McCain and Democrats Barack Obama and Hillary Clinton - will question Petraeus and Crocker directly and are expected to use the opportunity to air their views on the five-year-old conflict.

"RECKLESS" PLEDGES

McCain, the top Republican on the first committee set to grill Petraeus, said on Monday that progress from the surge strategy in Iraq was undeniable. He said his Democratic rivals were making "reckless" pledges that cannot be kept to quickly pull troops from Iraq.

But Obama, now leading the race for the Democratic nomination, said it would be a "failure of leadership" to have an open-ended commitment to Iraq.

Security gains in Iraq have been tenuous. U.S. military officials describe them as "fragile" and say they are easily reversible.

Intra-Shi'ite fighting in Baghdad and the southern oil city of Basra in recent weeks appears to underscore both the shaky security situation and the lack of progress toward political reconciliation, analysts said.

Those clashes have killed hundreds and driven civilian deaths in Iraq to their highest level in more than six months.

"If there is any clear message that emerges out of the events of the last few weeks, it is that the risks in Iraq remain high enough so that no one can yet say whether the odds of any kind of U.S. success are better than even," said Anthony Cordesman with the Center for Strategic and International Studies in Washington.

The United States now has 160,000 troops in Iraq. Under plans announced last year, the Pentagon is pulling five combat brigades - or about 20,000 troops - out by mid-July, bringing the force level down to what it was before the surge.

Many security analysts backed that decision, saying U.S. commanders need months to evaluate conditions after the surge. They also said they will look for Petraeus to present a strategy for tackling Shi'ite rivalry in the south, an area the United States has largely left to British and Iraqi troops.