"If we were to quit Iraq before the job is done, the terrorists we are fighting would not declare victory and lay down their arms. They would follow us here," Bush said at the West Virginia Air National Guard.
At the same time, an anti-war demonstration took place on the other side of the state in Charleston.
The war, in its fifth year, has claimed the lives of more than 3,580 US soldiers.
"It's a tough fight, but I wouldn't have asked those troops to go into harm's way if the fight was not essential to the security of the United States of America," Bush said.
In Baghdad, the administration was trumpeting a ceremony in which 588 US troops marked the holiday by re-enlisting Wednesday, and 161 soldiers took oaths making them American citizens.
However, difficulties continue in Iraq. Sunnis, Shia and Kurds said on Wednesday that they had not been able to agree on a draft bill to regulate the country's oil industry - something Washington hopes will rally Sunni support for the government and reduce backing for fighters.