"Too many variables" made it impossible to put the cost of military action against Iraq into President Bush's 2004 budget request sent to Congress Monday, a senior official told Fox News on Tuesday.

The official said that the administration will quickly estimate the cost of war and ask for the entire amount in an emergency spending request if the nation does launch action against Iraq, the official said.

So far, the president has not decided on any military action. However, once the president makes that decision, everyone will sit down and "agree on how many troops and for how long. No one knows, of course, but we will have to estimate it," the official said. "We'll have the most thoughtful estimate anyone can have and send it to Congress. "

Officials say they were not sure of the costs associated with events that unfolded after the Sept. 11, 2001 terror attacks, however the administration embarked on a similar process and ended up coming very close to the eventual cost of reconstruction and recovery.

Secretary of State Colin Powell is going to the United Nations on Wednesday to lay out evidence to prove that Iraq continues its program to assemble weapons of mass destruction. The Defense Department has already deployed thousands of troops to the Persian Gulf region that are in advanced position should military action occur.

Officials have divided the costs of war into four variables, including reimbursement and support for other countries who provide basing and other assistance of that nature; combat itself; the aftermath and withdrawal; and equipment and material replacement such as tanks, ammunition and the like.

A key official said it was very difficult to put a figure on what the price of war will be before a decision is made to go in, how many troops to commit and what the actual attack plan would involve.

Another official suggested that such thinking has taken place at the Pentagon but until a decision is made, White House officials will not be embracing any detailed estimates.

Fox News' Jim Angle contributed to this report.