March 19 (Bloomberg) -- President George W. Bush said today the extra forces he ordered into Iraq last year have increased security in the country and paved the way for a ``major strategic victory'' in the war against terrorism.

That progress has made the ``high cost in lives and treasure'' in Iraq worthwhile, the president said in a speech marking the fifth anniversary of the U.S.-led invasion.

Bush is arguing for continued U.S. involvement in Iraq to what polls show is a skeptical public. He also is confronting repeated attempts by Democrats in Congress to set a deadline for U.S. withdrawal.

``Successes we are seeing in Iraq are undeniable, yet some in Washington still call for retreat,'' Bush told an audience of Defense and State Department officials and military officers at the Pentagon. ``War critics can no longer credibly argue that we're losing.''

As Bush spoke, anti-war demonstrations were being staged in the capital and in other cities. While there were few arrests in Washington early in the day, authorities were shutting down a major intersection downtown this afternoon because of the demonstrations, said Officer Israel James of Washington's Metropolitan Police Department. Protesters also targeted federal offices, including the Internal Revenue Service.

Troop Reductions

Bush indicated he isn't ready to withdraw more troops than have been scheduled to leave through about mid-July. The Defense Department is withdrawing five of 20 combat brigades from Iraq, totaling about 20,000 soldiers. The U.S. has about 158,000 military personnel in Iraq after Bush boosted the number of troops last year.

He said that ``too fast a drawdown could result in such an unraveling'' that insurgents would regain lost ground and increase violence.

``We're not going to let this happen,'' he said.

The two contenders for the Democratic presidential nomination, Senators Hillary Clinton of New York and Barack Obama of Illinois, both have promised to begin withdrawing U.S. troops if elected.

``The fact is, there is no military solution to Iraq's civil war,'' Clinton said yesterday in Philadelphia.

Obama today took aim at Bush and Arizona Senator John McCain, the presumed Republican presidential nominee, for their stances that the U.S. must stay in the fight in Iraq.

U.S. Security

``Fighting a war without end will not force the Iraqis to take responsibility for their own future,'' Obama said at Fayetteville Technical Community College in North Carolina before an audience of military families and local officials. ``And fighting in a war without end will not make the American people safer.''

McCain, who visited Iraq during the weekend, released a statement saying the U.S. is ``on the precipice'' of a major victory there.

``The security gains over the past year have been dramatic and undeniable,'' McCain said.

Bush's speech was part of an administration effort to argue that the U.S. presence in Iraq must be sustained.

Vice President Dick Cheney, a day after addressing troops in Iraq, dismissed the weak support in the U.S. for the war.

Public Opinion

``So?'' he said, when asked in an interview with ABC News about public opinion polls showing two-thirds of Americans believe the war was not worth fighting.

``You cannot be blown off course by the fluctuation in public opinion polls,'' Cheney said in Oman. ``There has, in fact, been a fundamental change and transformation and improvement for the better.''

The president said there will be more fighting ahead as U.S. troops try to push al-Qaeda in Iraq out of strongholds near Mosul. While ``the gains we've made are fragile and reversible,'' he said, the levels of violence and deaths ``are down.''

General David Petraeus and Ambassador Ryan Crocker are scheduled to deliver a progress report on Iraq to Congress next month.

Bush said that before the deployment of 30,000 more troops last year, the mission in Iraq was ``faltering'' as terrorists and insurgents destabilized the country.

``The surge has done more than turn the situation in Iraq around; it has opened the door to a major strategic victory in the broader war on terror,'' Bush said. ``The challenge in the period ahead is to consolidate the gains we have made and seal the extremists' defeat.''

`Arab Uprising'

Because of the surge, ``We are witnessing the first large- scale Arab uprising against Osama bin Laden, his grim ideology and his terror network,'' Bush said. ``The significance of this development cannot be overstated.''

Bush criticizes congressional Democrats, who have attacked the money being spent on the war and derided what he called ``exaggerated estimates'' of its cost.

Congress has already appropriated more than $400 billion for military operations in Iraq. Nobel economics laureate Joseph Stiglitz told Congress's Joint Economic Committee last month that the war may end up costing the U.S. more than $3 trillion once all bills associated with the conflict come due.

In addition, at least 3,988 U.S. personnel have died in Iraq and 29,395 more have been wounded, according to Department of Defense figures.

``No one would argue that this war has not come at a high cost in lives and treasure,'' Bush said. ``But those costs are necessary when we consider the cost of a strategic victory for our enemies in Iraq.''

To contact the reporter on this story: Roger Runningen in Washington at rrunningen@bloomberg.net

Last Updated: March 19, 2008 16:04 EDT