Washington ? National Guard and Reserve members whose special skills would be needed in a war with Iraq might get advance notice of possible mobilization, even though President Bush has not yet decided whether to use military force, a senior Pentagon official said Tuesday.

Reservists would like some warning so they can make arrangements with employers and family members, even if the call to active duty never comes, said Thomas Hall, the assistant secretary of defense for reserve affairs. But there are concerns about such a plan, he said.

“If you elect to do that, then are you giving potential enemies and others advance information of what you’re going to do? Are you also unnecessarily alerting people that they might be mobilized, … and then it turns out they aren’t called up?”

Currently, 51,358 reservists are on active duty, most assigned to positions in the United States in the aftermath of the Sept. 11, 2001, attacks. That number peaked in late July above 85,000. If the United States goes to war in Iraq, Pentagon officials expect to need at least 100,000 more and possibly twice that.

Although Hall said the Pentagon has no list of reserve units likely to be called up, war in Iraq would demand a wide variety of reserve specialists, including linguists, special operations forces, military police and other security forces, pilots and logisticians.

Under the partial mobilization that President Bush authorized after the Sept. 11 attacks, as many as 1 million of the military’s 1.3 million reservists could be called to active duty for as long as two years.