US President George W Bush has vowed the US will not tire in its "war on terror", but acknowledged that more difficulties could lie ahead.
Mr Bush stuck to familiar themes and avoided domestic issues
His speech came amid flagging public support for the war in Iraq, where more than 2,000 US servicemen have died.
Mr Bush said he would accept nothing less than "complete victory" in the war on terror, which he described as the first great war of the 21st century.
Mr Bush, heckled during his speech, did not comment on his domestic woes.
Instead, much of his speech focused on the war on terror - a war, he said, where the stakes could not be higher.
"We don't know the course of our own struggle, where it will take us or the sacrifices that might lie ahead," he told his Virginia audience.
"But we do know however that the defence of freedom is worth our sacrifice.
"We do know the love of freedom is the mightiest force of history and we do know the cause of freedom will once again prevail."
He singled out Iraqi insurgent leader Abu Musab al-Zarqawi and al-Qaeda second-in-command Ayman al-Zawahiri as "enemies of freedom", adding that fostering democracy in Iraq would require an "untiring vigil".
In a passionate speech revisiting familiar ground, Mr Bush invoked the memory of 9/11 in his defence of US policy, reminding his audience that the US was attacked in 2001 long before the invasion of Iraq.
"Tyrants and would-be tyrants have always claimed that murder is justified to serve their grand vision and they end up alienating decent people across the globe," he said.
"And tyrants and would-be tyrants have always claimed that free men and women are weak and decadent, until the day that free men and women defeat them."
Mr Bush spoke hours before a special prosecutor announced whether two senior White House aides faced criminal prosecution over the unmasking of a covert CIA agent's identity.
On Thursday the president's nomination to the Supreme Court, Harriet Miers, withdrew from consideration amid bi-partisan opposition.
Mr Bush prompted laughter in the crowd when he told his Virginia audience that it was "nice to get out of Washington".