He had signed a similar order on Saturday to send 35,000 troops, most of whom are now already on their way to the region.
With the latest deployment, the strength of US troops in the Gulf will reach 150,000.
On the other hand, the Pentagon and US intelligence agencies have increased their e-mail messages to government officials in Iraq, urging them to ditch President Saddam Hussein.
The message also instructs them how to contact the United Nations if they want to defect.
Messages were sent to President Saddam’s close associates, ministers and generals, officials in Washington said.
On Saturday, US Secretary of State Colin Powell warned that the United States “reserves the right, in the absence of international action to disarm Iraq, to act with like-minded nations to disarm Iraq”.
His comments followed a UN report saying that its inspectors had found “no smoking guns” in Iraq during their recent investigations. The report caused speculations in the US media that this would make it more difficult for Washington to get international endorsement for a military action.
New deployment includes navy and air force troops. They follow the Marines, some of whom left their bases for Iraq on Saturday. In case of a military offensive, the Marines will lead the attack.
As the Bush administration increases its military might in the Gulf, peace and human rights groups at home also have increased their protest against the war.
The largest rally this weekend was held in Los Angeles, where almost 20,000 people turned up to demonstrate against the administration’s military policies.
This was the largest anti-war demonstration in Los Angeles since the Vietnam war.
Similar rallies will be held in other American cities.
Peace activists also have planed a major rally in the US capital on Jan 18 and have urged supporters across the United States to participate.