The Army, pressed by unusually high demand for special forces in Afghanistan, invoked a rarely used authority to stop about 1,000 soldiers from leaving the service, officials said Tuesday.

It was the first time the Army has used this authority since 1990, when the Pentagon was building up large forces in Saudi Arabia and the Persian Gulf in preparation for war against Iraq in Kuwait.

Special forces members, commonly called the Green Berets, train, equip and supervise foreign forces and can conduct direct combat missions.

A few hundred special forces in Afghanistan have worked extensively with the Northern Alliance troops opposing the Taliban. They have been credited with helping find and designate targets for U.S. attack planes.

The Army's order, which took effect Monday, does not affect other special operations troops such as Rangers. Nor does it affect members of the reserves who have not been called to active duty.

Soldiers affected by the order, known as "stop-loss," may not retire or leave the service, although some soldiers scheduled to leave prior to Jan. 15 may be allowed to do so, Army officials said.

"The intent is to ensure the Army does not create hardship for soldiers who have begun transition leave," said Lt. Col. Robert Ortiz of the office of the deputy chief of staff for personnel.

He said an estimated 994 soldiers will be affected through Sept. 30, 2002.

The Air Force and Navy began limited use of the "stop-loss" authority in October. Defense Secretary Donald H. Rumsfeld delegated the authority to the service secretaries on Oct. 13.

Among the troops affected by the Army order are key members of what the special forces call their "A" team, 12 men who are multilingual and trained in many specialties.

Others affected include communications specialists, medics, demolitions experts, weapons specialists, helicopter maintenance specialists and helicopter pilots.