London ? Britain is preparing to commit up to 20,000 troops to join U.S. forces in a war against Iraq. But it is not likely that the British forces will be in place until late February or the beginning of March, according to defense analysts.

U.S. military planners are contemplating a somewhat earlier timetable, with Jan. 27 — the date by which chief U.N. weapons inspector Hans Blix must report to the Security Council — frequently cited as a potential “trigger” day.

An estimated 50,000 U.S. troops are in the region, with another 50,000 soon to be on the way, as President Bush increases the pressure.

British Prime Minister Tony Blair has told his armed forces to prepare for war, but he is not expected to give the order to deploy until after the Security Council acts on Blix’s findings. Once the order is given, it will take at least three weeks for the troops and equipment to get into position and gear up to a state of full combat readiness.

“There’s a political element to the timing. The U.K. government will have tremendous difficulties if it doesn’t look as though it has exhausted the U.N. process,” said Timothy Garden, director of the Royal Institute of International Affairs, a London research center.

“The British public is not desperately enthusiastic about this campaign, and if the U.S. wants Britain with it, which I think it does, it will have to take this into consideration,” Garden said.

Blair wants Britain to be a significant partner rather than a bit player in any military action against Iraq. To that end, Britain is planning to contribute an armored division, an aircraft carrier battle group and a significant Royal Air Force component to the U.S. buildup under way in the Persian Gulf.