WASHINGTON, March 6 — President Bush will hold a prime-time news conference tonight to discuss his determination to disarm Iraq and the campaign against terrorism, the White House announced today.

The televised session will begin at 8 p.m. Although tensions over Iraq have been high and war looms as a distinct possibility, the chief White House spokesman, Ari Fleischer, emphasized this morning that the president would not make a momentous announcement.

For a time this morning, there were rumors in the capital that Mr. Bush would announce the capture of the most wanted of all terrorists, Osama bin Laden. But several officials quickly sought to knock down those rumors, and Mr. Fleischer himself discouraged speculation. .

"This is a news conference," Mr. Fleischer said. "This is not a scheduled announcement of anything."

Amid the deepening tensions between Washington and some traditional American allies over what to do about Iraq, and how long to wait before deciding that military force is necessary, the president and his aides are still savoring the capture in Pakistan last weekend of Khalid Sheikh Mohammed, the operations chief of Al Qaeda.

American intelligence officials have expressed the hope that Mr. Mohammed, who is being interrogated in an unknown location, might yield information that would lead to the capture of other terrorists.

Even if Mr. Bush makes no startling announcement tonight, there was no mistaking the seriousness of the situation. His news conference comes on the eve of a critical meeting of the United Nations Security Council to discuss the extent of Iraqi compliance with disarmament requirements.

And it comes a day after France, Germany and Russia presented a unified front against an American-led military campaign against Iraq. France and Russia said they are ready to use their veto powers, as permanent members of the Security Council, to block passage of a new resolution authorizing force against Baghdad.

Tonight's news conference will be only the second such prime-time event in the White House East Room since Mr. Bush took office. The first was soon after the terror attacks of Sept. 11, 2001.

Mr. Fleischer said the president would make an opening statement about the campaign against terrorism and the need to disarm Saddam Hussein. In recent months the Bush administration has portrayed the two endeavors as intertwined.

The president and his top aides have said repeatedly that force would only be used against Iraq as the very last resort. Mr. Fleischer restated that theme today, but he added, "In the event that the president decides to use force, the president always thinks it's important to communicate."