WASHINGTON (AP) _ The military is taking a hard look at the future of combat reserves after failing to get National Guard units battle-ready in time to fight in the Persian Gulf War, Gen. Colin Powell said Friday.

The chairman of the Joint Chiefs of Staff, speaking to the National Newspaper Association, said it was evident reserve units will require more training before they can join active-duty troops on the battlefield.

''What we're looking at now is how much additional training do units such as that require and how do we package them in the force in the best possible way,'' he said.

A senior Defense Department official later said the Army may have to reconstitute the 24th Infantry Division (Mechanized), which is part of the Army's rapid deployment force, to make it exclusively active duty. It currently has two active-duty brigades and one reserve, or ''roundout'' unit, the 48th Infantry Brigade of the Georgia National Guard, which was called up for the Persian Gulf crisis but never got to the war.

''The roundout brigades may not be useful for immediate, crisis response,'' said Christopher Jehn, assistant defense secretary for force management and personnel, because they require too much training time before deploying.

''I'm sure one of the things the Army will want to do is to make sure those divisions that wind up having roundout brigades are not considered part of the immediate contingency force,'' Jehn said in an interview.

The delay in dispatching three Army National Guard combat brigades to the gulf because of inadequate training came amid general praise for other contributions by the reserves.

Of the 105,000 reservists from all the services deployed to the gulf, most were involved in support jobs such as mechanics, truck drivers, accountants, hospital workers and water purification experts.

The National Guard combat units in question were formed under the ''roundout'' concept under which combat reserves can quickly join up with partner active-duty units on the field.

''It is simply a fact of life that a combat unit such as an infantry or armored brigade requires a great deal of intense training when called for active duty,'' Powell said. Ensuring that a guard unit will be able to integrate and use all the weapons available to them ''is more than we can expect the guard units to do in 39 days of training.''

Secretary of Defense Dick Cheney told The Los Angeles Times earlier in the week that future Army rapid-deployment divisions should be composed entirely of active-duty forces.

''We ought to use the guard combat units as a second or third echelon that you call up and deploy over a longer period of time. The planning would take into account not that they deploy the first day of the war but rather that they get 90 days, 120 days of work-up before you send them,'' Cheney said.

One of the three roundout units, the 48th Infantry Brigade (Mechanized) from the Georgia National Guard, was mobilized Nov. 30 and sent to Fort Irwin's National Training Center in California. But its training period was extended several times and the war ended before the unit was judged ready for combat.

The former commander of the 4,500-member unit, Brig. Gen. William A. Holland, was relieved of his duties. He later complained the unit was mobilized for political reasons and was resented by regular Army personnel who opposed the roundout concept.

The assistant secretary of defense for reserve affairs, Stephen M. Duncan, said in an interview that the roundout concept ''has a very positive future.''

But he, too, stressed that larger ground combat units - brigades and divisions - will need more training time if they are to synchronize with active-duty troops in handling complex air-and-ground maneuvers.

Duncan said the three roundout brigades comprised only about 10,000 of the 150,000 Army reservists and National Guard members called up for Desert Shield and Desert Storm.

Since the 1970s the military has adhered to a ''total force'' policy in which an all-volunteer army is backed up by a large and well-trained reserve force and civilian workers. The Persian Gulf War led to the first large-scale call-up of the reserves in more than two decades.