RESERVES SWEPT TO FRONT LINE.

Byline: Mike O'Connor The New York Times

As the U.S. peacekeeping mission in Bosnia continues to eat away at military resources, the number of reservists and National Guard members thrust into military life is growing sharply.

More Army reservists have been called up for active duty on the NATO-led force in Bosnia than were called during all of the Vietnam War. And for the first time in nearly three decades, a National Guard combat unit has been sent overseas. About one-third of all U.S. forces now in Bosnia are reservists and members of the National Guard.

The increasing resort to reservists stems from the Army's sharp reduction in personnel - 50 percent in just this decade. In 1990, as the Cold War was winding down, there were about 2 million soldiers in the active-duty Army, the Army Reserve and the Army National Guard combined. Today there are 993,000.

At the same time, the number of peacekeeping missions has increased, not only taxing the active-duty Army, but also drawing on many of the specialties now found predominantly in the Reserve.

One of the reservists serving in Bosnia is Chief Petty Officer Milinda Jensen of the Navy.

The other day, she straightened the shoulder holster strapped over her camouflage uniform. She tugged the 9 mm Beretta automatic pistol hanging from one side, and on the other side pulled on the two ammunition cases, each holding 14 rounds.

With that, she began to lead a classroom of 12- and 13-year-olds in boisterous games. Then she described a day in the life of an American family.

As she showed the children photographs of her family on vacation, Marko Katic, 12, the son of a leader in the hard-line Bosnian Serb political party, jumped to his feet. ``My dream has always been to have a vacation in Yellowstone Park in America,'' he said in halting but energetic English.

This was not Jensen's regular duty in Bosnia. As a reservist, she was plucked from her civilian life as a public school teacher in Virginia and assigned to help run a NATO public information center in Bosnia. She was in the classroom on her time off because she wants to learn about the Bosnian people and wants them to learn about the United States.

When Jensen became one of the 3,500 reservists and members of the National Guard now mobilized for Bosnia, she was given little choice whether to go or what her job would be.

Pentagon's hopes

But while some of her colleagues resent having been called up, Jensen, 43, represents what the Pentagon hopes to find among the ranks of Americans in the Guard or Reserve mobilized for lengthy missions overseas.

Jensen switched to the Naval Reserve from active duty, and her husband is a Navy retiree. They live with their 17-year-old daughter in Norfolk, Va. ``As a family we are used to this,'' she said. ``I like the adventure.''

The Army's thinner ranks and new peacekeeping mission have caused what senior officers call a fundamental change in how the military views the forces at its disposal. It is no longer a case of drawing on active personnel first and the Reserves and National Guard only in emergencies.

``Everyone is in the pool,'' said Brig. Gen. Pat O'Neal. ``They are all eligible to go. That's the change.'' As a deputy commander of Forces Command, O'Neal is one of the top officers deciding which units are sent where.

The change is already being felt widely, and next year twice as many Guard and Reserve members are expected to be sent overseas.

Many officers and soldiers in Bosnia say that will reveal the flaws of the new policy. They are already asking how often and for how long civilians will put up with being taken away from their families and careers and dispatched to hazardous, low-paying jobs in other countries.

``The Army's senior leadership has those same kinds of questions,'' said Brig. Gen. James Helmly, deputy chief of the Army Reserve, in a telephone interview from the Pentagon. ``They are having a lot of late nights trying to answer them.''

Members of the Reserves and the National Guard receive moderate pay and other benefits in return for active service one weekend a month and two weeks a year.

They can be called on for much longer active duty by the president. Usually, the higher pay they receive when mobilized is considerably less than what they earn in their civilian jobs.

Job concerns

Employers are barred from discriminating against employees called up for active service. But many reservists say the law is difficult to enforce, and they worry about what will happen if they are mobilized for months at a stretch.

``My boss told me straight out, `If I can get along without you for a few months, I guess I can just plain get along without you,' '' said one sergeant in the Reserves who spoke on condition of anonymity.

Some reservists in Bosnia have been assigned tours of more than six months, and many say their families and employers do not understand the reasons for their absence.

With the end of the Cold War, the United States has not only reduced the size of its military but also increased the number of places to which it has sent troops overseas. This month the Army alone has 33,944 soldiers on temporary duty in 81 foreign countries. Most are on peacekeeping missions or training exercises.