WASHINGTON — Democrats and moderate Republicans in Congress have tough questions for a top military commander in Iraq who is warning against major changes to President Bush's war strategy.

Gen. David Petraeus and Ambassador Ryan Crocker were scheduled to testify today in the first of three hearings this week on the future course of the unpopular 4-year-old war.

Officials familiar with their thinking told The Associated Press over the weekend that the advisers will acknowledge disappointing progress in Prime Minister Nouri al-Maliki's bid to achieve national reconciliation but would urge Congress to maintain the U.S. troop buildup to preserve local security gains.

On Sunday, Democrats sharply questioned Bush administration assertions that seven months of troop increases might be working, citing continuing violence and al-Maliki's political woes. They said they would not back off efforts to set target dates for bringing troops home.

"The reality is that, although there has been some mild progress on the security front, there is, in fact, no real security in Baghdad or Anbar province," said Sen. Joseph Biden, D-Del., a 2008 presidential candidate who chairs the Senate Foreign Relations Committee.

Pennsylvania Sen. Arlen Specter, a moderate Republican, said he respected Petraeus' judgment but would not blindly follow it.

"We're going to look behind the generalizations that General Petraeus or anybody gives us and probe the very hard facts to see exactly what the situation is," Specter said. "As I've said in the past, unless we see some light at the end of the tunnel here, very closely examining what General Petraeus and others have to say, I think there's a general sense that there needs to be a new policy."

In their long-awaited report to Congress, Petraeus and Crocker will say the buildup of 30,000 troops, which brings the U.S. total to nearly 170,000, is working better than any previous effort to quell the insurgency and restore stability, according to the officials who spoke on condition of anonymity because they were discussing internal deliberations.

The officials also disputed suggestions that Petraeus and Crocker would recommend anything more than a symbolic reduction in troop levels and then only in the spring.

The testimony sets the stage for an announcement by Bush later in the week about how he will proceed in the face of growing congressional discomfort with the war.

Biden said Petraeus' assessment missed the point. Biden said focusing on a political solution, such as by creating more local control, was the only way to foster national reconciliation among warring factions.

"I really respect him, and I think he's dead flat wrong," Biden said.

Biden contended that Bush's main strategy was to buy time and extend the troop presence in Iraq long enough to push the burden onto the next president, who takes office in January 2009, to fix the sectarian strife.

"This president has no plan — how to win and how to leave," Biden said.

But Sen. Lindsey Graham, R-S.C., said he trusts the military judgment of Petraeus and that it was foolish for Congress to try and second-guess commanders on the ground.

Meanwhile, a New York Times/CBS News Poll found that Americans trust military commanders far more than the Bush administration or Congress to bring the war in Iraq to a successful end.

Five percent of Americans said they most trust the Bush administration to resolve the war, the poll found; 21 percent said they would most trust Congress; and 68 percent expressed the most trust in military commanders.