B-52 bombers are being sent to the Gulf
US Army Secretary Thomas E White told a briefing at the Pentagon that the deployment order signed by Defense Secretary Donald Rumsfeld on Wednesday included army as well as air force troops.
He said the army was ready to conduct "sustained land combat operations".
Mr White said it was only the first step in a broader military plan that would unfold in the weeks ahead.
"A lot more will come," he said.
Also speaking at the Pentagon, Mr Rumsfeld refused to be drawn on details of the deployment, but said: "We are trying to get ourselves arranged in the world, with our forces, in places that we believe conceivably could be useful in the event the president decided to use them."
'Air bridge'
The air force is sending more than 100 aircraft to the Gulf, said to include F-16 and F-15 fighters and B-52 bombers and well as tanker aircraft to create an "air bridge" to refuel the combat planes.
Mr Rumsfeld also said they were reconsidering the name given to the military deployment, "Operation Infinite Justice," because in the Islamic faith only Allah can provide infinite justice.
Mr White said "all combat capabilities" would be included in the US deployment.
The aircraft carrier USS Theodore Roosevelt and the ships in its battle group left their home port at Norfolk, Virginia, on Wednesday for a scheduled six-month deployment to the Mediterranean.
The battle group includes 2,100 Marines aboard a battle-ready unit known as an Amphibious Ready Group, led by the assault ship USS Bataan.
There are also two attack submarines, the USS Hartford and the USS Springfield, which can fire Tomahawk cruise missiles.
The US Navy has a carrier battle group in the Gulf - the USS Carl Vinson - and a second, the USS Enterprise, is in the Arabian Sea to the south.
Intelligence operations
But BBC defence correspondent Jonathan Marcus says the military dimension will be only part of a much broader effort to disrupt and destroy the shadowy networks behind the US hijackings.
Intelligence agencies and law-enforcement organisations in several countries will have a part to play.
Other secretive preparations - involving intelligence operations using satellites and electronic eavesdropping will also be under way.
Special forces will also have an important role - there could be significant deployments of such units - signalling that for the Americans this is indeed a new sort of war where there is no reluctance to place US soldiers in harm's way.
The diplomatic coalition being forged to back Washington has a practical side as well as the purely rhetorical.
Information exchanges will have to be stepped up; computer and financial experts deployed to track terrorist funds. It is easy to concentrate on the movement of military hardware - aircraft carriers leaving port cannot be hidden.
But much of the real war will be taking place in the shadows and it will not be talked about in the press briefings either.