The U.S. military build-up now under way in the Gulf region will take several more weeks to reach the 150,000 mark.

A senior U.S. military official says the bulk of the troops now moving to the Gulf come from a group of 25,000 whose deployment was ordered last month by Defense Secretary Donald Rumsfeld.

This official, speaking on condition of anonymity, says it will take several more weeks before the next big batch of forces heads to the region. These are the 62,000 whose deployment was ordered by Mr. Rumsfeld late last week.

These large deployments, added to the 60,000 soldiers, sailors, airmen and marines already in the Gulf, will push the total American force poised to confront Iraq to close to 150,000.

Some Pentagon sources say that number could eventually rise to 250,000.

Defense officials stress President Bush has made no decision about going to war with Iraq.

But they say the deployments ordered by the Pentagon are intended to give Mr. Bush the option to use force if necessary, perhaps by the end of February. Key members of the military's battle planning staff have already begun moving to a base in the Gulf state of Qatar where a crucial command-and-control center has been established.

In the meantime, the U.S. military is already conducting so-called psychological operations aimed at turning Iraqi public opinion against President Saddam Hussein.

The operations carried out so far include radio broadcasts and an e-mail campaign aimed at the computers of top Iraqi military and civilian officials.

The senior Pentagon official says such efforts could stir sufficient internal dissent to trigger a coup against the Iraqi leader or force him into exile, moves which could eliminate the need for any military confrontation with the United States.

The official concedes Saddam Hussein is a well-entrenched, wily survivor who is probably not vulnerable. But he says sowing dissent, particularly in military ranks, is worth the effort.

Part of the campaign is aimed at persuading Iraqi authorities not to use chemical and biological weapons against U.S. troops if there is a war.

The possible use of such weapons of mass destruction is one of the major concerns of U.S. military planners.