President Bush plans to tell the nation Thursday night that he intends to reduce the American troop presence in Iraq by as many as 30,000 by next summer, but those and further cuts will be conditioned on continued progress.

The president, who will deliver a 15-minute address from the White House at 9 p.m. EDT, will endorse the recommendations of his top general and top diplomat in Iraq, following their appearance at two days of hearings in Congress, administration officials said. The White House plans to issue a written status report on the troop buildup on Friday, they said.

Ahead of the president's speech, Secretary of State Condoleezza Rice said Wednesday the end goal is to reduce the U.S. troop footprint while considering Iraq's overall stability, including "the territorial security of Iraq" — with a strong eye cast toward it's northern neighbor, Iran.

"Iran is a very troublesome neighbor," Rice said, speaking on NBC's "Today" show. "Iran is prepared to fill the vacuum" if the United States leaves Iraq.

"That is what is at stake here," Rice said. "What we are prepared to do is to complete the security gains that we've been making, to create circumstances in which an Iraqi government and local officials can find political accommodation, as they are doing in Anbar, and to be able then, from Iraq, with allies in the war on terror, to resist both terrorism and Iranian aggression."

The White House officials, who spoke on condition of anonymity because Bush's speech is not yet final, said the president was rehearsing and polishing his remarks even as the U.S. commander in Iraq, Gen. David Petraeus, and U.S. Ambassador Ryan Crocker were presenting their arguments for a second day on Capitol Hill.

In the speech, the president will say he understands Americans' deep concerns about U.S. involvement in Iraq and their desire to bring the troops home, administration officials said. Bush will say that, after hearing from Petraeus and Crocker, he has decided on a way forward that will reduce the U.S. military presence but not abandon Iraq to chaos.

Democrats have requested network air time following Bush's speech to lay out a response. Sen. Jack Reed, D-R.I. — a member of the Senate Armed Services committee and former Army Ranger — is expected to deliver the response

Meanwhile, Reuters reported that Iraq's national security adviser believed the number of multinational forces in Iraq could drop to less than 100,000 by the end of next year if Iraq's own security forces were ready.

"Maybe it is not far from the truth if we said that by the end of next year, multinational forces could be less than 100,000," Mowaffaq al-Rubaie told a news conference.

Bush's address is expected to stake out a conciliatory tone toward Congress. But while mirroring Petraeus' strategy, Bush will place more conditions on reductions than his general did, insisting that conditions on the ground must warrant cuts and that now-unforeseen events could change the plan.

Petraeus recommended that a 2,000-member Marine unit return home this month without replacement. That would be followed in mid-December with the departure of an Army brigade numbering 3,500 to 4,000 soldiers. Under the general's plan, another four combat brigades would be withdrawn by July 2008.

That could leave the U.S. with as few as 130,000-135,000 troops in Iraq, down from about 168,000 now, although Petraeus was not precise about whether all the about 8,000 support troops sent with those extra combat forces would be withdrawn by July.

Petraeus said he foresaw even deeper troop cuts beyond July, but he recommended that Bush wait until at least March to decide when to go below 130,000 — and at what pace.

At the White House, Bush met with House and Senate lawmakers of both parties and he publicly pledged to consider their views. Senate Minority Leader Mitch McConnell, R-Ky., said the president didn't talk about the nationwide address.

House Speaker Nancy Pelosi, D-Calif., said Bush appears poised merely to bring the country back to where it was before the election that put Democrats in control of Congress — with 130,000 troops in Iraq.

"Please. It's an insult to the intelligence of the American people that that is a new direction in Iraq," she said.

In his speech, Bush will adopt Petraeus' call for more time to determine the pace and scale of future withdrawals and offer to report to Congress in March, one official said.

As Petraeus and Crocker have, Bush will acknowledge difficulties, and the fact that few of the benchmarks set by Congress to measure progress of the buildup have been met, the official said. Yet, he will stress that a precipitous U.S. withdrawal would be a catastrophe for Iraq and U.S. interests.

The president will discuss "bottom up" security improvements, notably in Anbar Province, which he visited on Labor Day and where Sunni leaders have allied themselves with U.S. forces to fight insurgents. And, he will note incremental progress on the political front despite unhelpful roles played by Iran and Syria, the official said.

Crocker was particularly keen on detailing diplomatic developments, including Saudi Arabia's move to open an embassy in Baghdad and a third conference of Iraqi neighbors to be hosted by Turkey in Instanbul at the end of October.

In Congress, cracks in Republican support for the Iraq war remained, as epitomized by heated questioning Tuesday of Petraeus.

"Is this a mission shift?" asked Sen. Lisa Murkowski, R-Alaska. "Are we continuing down the same path that we have laid out before, entirely reliant on the ability of the Iraqis to come together to achieve that political reconciliation?"

Sen. Norm Coleman, R-Minn., said he wants a longer-term vision other than suggestions that Petraeus and Crocker return to Capitol Hill in mid-March to give another assessment. "Americans want to see light at the end of the tunnel," said Coleman.

Democrats, under substantial pressure by voters and politically influential anti-war groups, had anticipated that a larger number of Republicans by now would have turned against Bush on the war because of grim poll numbers and the upcoming 2008 elections.

Indeed, Petraeus' testimony helped to solidify support elsewhere in the GOP, keeping Democrats far from the 60 votes they needed to pass legislation ordering troops home.

"Americans should be happy that we can begin to reduce troop levels months ahead of schedule," said Sen. Pete Domenici, R-N.M.

"I'm optimistic that when the votes are counted, they'll be roughly the same as they have been all year," said McConnell, the Senate Republican leader. "As you know, we've lost some, but not a lot and I think that's a likely outcome again."

Echoing testimony given to the House on Monday, Petraeus and Crocker acknowledged that Iraq remains largely dysfunctional but said violence had decreased since the influx of added U.S. troops.

Crocker said he fears that announcing troop withdrawals, as Democrats want, would focus Iraqi attention on "building the walls, stocking ammunition and getting ready for a big nasty street fight" rather than working toward reconciliation. "It will take longer than we initially anticipated" for Iraq's leaders to address the country's problems, he said.

The two days of testimony seemed to turn the debate away from the list of 18 benchmarks by which the White House and Iraq's government had said earlier this year that they preferred to measure progress. The administration has protested more recently that the benchmarks offer an unrealistic or incomplete look at the situation.

The hearing fell on the anniversary of the Sept. 11, 2001, terrorist attacks.

In an unusual admission, Petraeus said he was not sure whether his proposal on Iraq would make America safer.

A visibly heated Sen. John Warner, R-Va., asked the question to which Petraeus said: "Sir, I don't know, actually. I have not sat down and sorted that out in my mind. What I have focused on and riveted on is how to accomplish the mission of the multinational force Iraq."

The Associated Press contributed to this report.