Bush went before Congress to ask for permission to use "all means (Bush) determines to be appropriate, including force, to enforce United Nations Security Council resolutions, "defend the national security interests of the United States against a threat posed by Iraq, and restore international peace and security in the region".
The US has not declared war according to provisions provided in the Constitution since WWII. In 1973 the US Congress passed the War Powers Act. Under this legislation a President has 90 days after introducing troops in an armed conflict to get Congressional approval.
The Congress granted Bush what he asked for in the COngressional Resolution on Iraq passed in October 2002. Under this resolution, the President "is authorized to use the Armed Forces of the United States as he determines to be necessary and appropriate in order to
1) defend the national security of the United States against the continuing threat posed by Iraq; and
(2) enforce all relevant United Nations Security Council resolutions regarding Iraq.
(b) PRESIDENTIAL DETERMINATION- In connection with the exercise of the authority granted in subsection (a) to use force the President shall, prior to such exercise or as soon thereafter as may be feasible, but no later than 48 hours after exercising such authority, make available to the Speaker of the House of Representatives and the President pro tempore of the Senate his determination that
(1) reliance by the United States on further diplomatic or other peaceful means alone either (A) will not adequately protect the national security of the United States against the continuing threat posed by Iraq or (B) is not likely to lead to enforcement of all relevant United Nations Security Council resolutions regarding Iraq; and
(2) acting pursuant to this resolution is consistent with the United States and other countries continuing to take the necessary actions against international terrorists and terrorist organizations, including those nations, organizations or persons who planned, authorized, committed or aided the terrorists attacks that occurred on September 11, 2001.
(c) WAR POWERS RESOLUTION REQUIREMENTS-
(1) SPECIFIC STATUTORY AUTHORIZATION- Consistent with section 8(a)(1) of the War Powers Resolution, the Congress declares that this section is intended to constitute specific statutory authorization within the meaning of section 5(b) of the War Powers Resolution.
(2) APPLICABILITY OF OTHER REQUIREMENTS- Nothing in this resolution supersedes any requirement of the War Powers Resolution.
SEC. 4. REPORTS TO CONGRESS.
(a) The President shall, at least once every 60 days, submit to the Congress a report on matters relevant to this joint resolution, including actions taken pursuant to the exercise of authority granted in section 3 and the status of planning for efforts that are expected to be required after such actions are completed, including those actions described in section 7 of Public Law 105-338 (the Iraq Liberation Act of 1998). "
See
http://hnn.us/articles/1282.html for full text