President Bush plans to reduce troop levels in Iraq by 5,700 by the end of December, and wants to draw down from 20 combat brigades there now to 15 brigades there by next summer, Bush said in a preview of his speech with network anchors Thursday.

Bush will address the nation in a speech from the Oval Office, and he is expected to say the surge he ordered in January has helped protect the Iraqi people from vicious attacks and is tamping down the worst of the sectarian violence seeking to tear the country apart.

Watch Bush's speech live on FOX News Channel or FOXNews.com at 9 p.m. ET, and watch the Democratic response delivered by Sen. Jack Reed immediately afterward streaming live on FOXNews.com.

In the lunch meeting with the news anchors, Bush said he wants to build a long-term strategic relationship with Iraq, and the Iraqi government also has asked for this. Bush pointed to South Korea and Afghanistan as models of that relationship: There would be a military presence there beyond his presidency, and Bush is trying to lay groundwork for a relationship between the two governments no matter who is president.

Bush will point to testimony given earlier this week by Gen. David Petraeus and Ambassador Ryan Crocker to say trends are moving in the right direction, and are heading in the way that could break the cycle of violence there, administration officials said earlier Thursday.

The president will say the surge has allowed for several more months of training of the Iraqi security forces, another key element Bush said was necessary for Iraqi political reconciliation.

Bush also is expected to discuss the death of Sunni Arab leader sheik Abdul-Sattar Abu Risha, who was killed along with two others by assassins on Thursday. Risha, whom Bush met with little more than a week ago when he touched down in Iraq for a surprise visit, was an example of leaders peeling away from Al Qaeda to work with American forces.

Click here to read more developments about sheik Abu Risha.

The president has a number of audience he's trying to address in the speech, administration sources said, including the American people, Congress, the Iraqi government, leaders around the Middle East, and Al Qaeda.

And most importantly, aides say, he will try to answer the question "Why does this matter?"

Petraeus' testimony earlier this week was one of the most highly anticipated hearings by a military commander since the Vietnam War, and the importance of tonight's speech has not been lost on the president, aides say: Bush has been through at least 20 drafts of the speech so far and has practiced it several times.

Thursday night's speech marks the eighth national address the president has made on Iraq since the March 2003 invasion of the country. His popularity over the war's handling has plummeted from heights of 75 percent down to about 20 percent now — although this week's testimony by his top deputies in Iraq has given him a slight boost.

Bush's speech, expected to last about 18 minutes, will be debated heavily both on Capitol Hill and on the White House campaign trail. Democrats have chosen Sen. Jack Reed, D-R.I., to deliver the party's response immediately following the president. Reed is one of the Democrat's top voices on military policy as a member of the Armed Services Committee and a former Army Ranger.

Former senator John Edwards, who is vying for the Democratic presidential nomination, has bought time on at least one cable network, MSNBC, to air an ad discuss Iraq plans after the president's speech.

The administration on Wednesday tried to get out in front of Democrat-led criticism of the president's plans. Democrats are saying the planned troop reductions only bring force levels down to what they were before the surge; Democrats argue they should go further.

Those criticisms don't apply, said White House press secretary Tony Snow.

"You don't have the same country you had in 2006. You're assuming nothing has changed. ... What Gen. Petraeus is saying is that you're able to move forces as a result of success," Snow said.

Democrats on both sides of Congress, however, had little support to offer the president.

"It appears the president's dug in, unwilling to recognize that his strategy is placing all the burden on our military, and it's simply not working," Senate Majority Leader Harry Reid told reporters Wednesday afternoon.

"His plan is neither to draw down, nor a change in mission that we need. His plan is simply more of the same: to keep at least 130,000 troops — American troops — in the midst of an intractable civil war. This is unacceptable to me, unacceptable to the American people," Reid said.

And possibly previewing his remarks to follow the president's, Reed said: "We have to go further. We have to limit our missions in Iraq, and we have to go ahead and recognize the strain on the military forces."

Reed said the troops should be limited to counterterror missions, force protection and training in Iraq.

"We have spent a huge amount of money, but more importantly, we have spent the lives of young Americans. Because of their sacrifice of service, they need a change of direction, a change in policy," Reed said.

This week, Petraeus and Crocker told lawmakers that violence in Iraq is down, there are increasing signs of stability, and troops can begin to come home. They admitted that political progress in Iraq — one of the chief purposes of sending the additional 30,000 troops into Iraq this year — has stagnated, and they declined to answer what they would recommend if the political situation remained this way midway through next year.

Petraeus said he could immediately begin withdrawing one Marine expeditionary unit, and by mid-July, 2008, would recommend bringing home five combat brigades plus to more Marine battalions sent to support Bush's troop surge plan that he laid out in January. That would bring the current level of troops — standing at about 169,000 — down to roughly 130,000.

The administration will take on a media blitz after Thursday's speech to support its position. Bush on Friday will head to the Marine base in Quantico, Va., to deliver remarks. Vice President Dick Cheney will head Friday to the Gerald R. Ford Presidential Museum in Michigan and MacDill Air Force Base in Florida. And Bush will discuss Iraq in his weekly Saturday radio address. The Sunday news talk shows will be peppered with administration officials.

FOX News' Chris Wallace, Wendell Goler and Bret Baier and The Associated Press contributed to this report.