WASHINGTON, Aug. 5 — The Army, stretched by commitments in Iraq and stretching to prove it can be as nimble as the Air Force, the Navy and the Marine Corps, is undertaking dramatic changes in the way it organizes and deploys troops in combat, a senior Army general said today.

An example of what is ahead for the oldest and largest armed service — and the one that has suffered criticism from Defense Secretary Donald H. Rumsfeld's inner circle — is the formation of a new way to "package forces" for Iraq, said Gen. John M. Keane, the Army vice chief of staff.

Soldiers from a number of different units and specialties will be mixed and matched and then brought together under one commander.

The skills offered by those troops — light infantry from the 82nd Airborne Division, unconventional warfare tactics of the Green Berets, community-building resources of civil affairs troops and military police to bring order — were specifically tailored for the mission in Iraq, General Keane said.

The general said "some pretty profound implications" emerged from the war in Iraq, a conflict in which all of the armed services fought in a joint fashion as never before, illustrating "organizational changes that the Army must make."

"The current force which we have right now — we have to take a look at making it more modular, more adaptable, and maybe some of those formations need to be smaller," General Keane said at a breakfast meeting with military affairs writers.

General Keane said the fresh unit was formed in consultation with Gen. John P. Abizaid, the new commander of allied forces in Iraq. The force will include troops not yet deployed and others already on the ground.

After the meeting, a senior Army official said that the combined force will be slightly smaller than a full division and will replace remaining members of the Third Infantry Division, which spearheaded the capture of Baghdad.

Also strengthening the unit will be a company of tanks, two companies of armored fighting vehicles and many Humvees, all from a mechanized brigade based at Fort Riley, Kan. Those vehicles and some helicopters will give the force protection and mobility, important for searching urban areas, an official said.

Although some in the Army resisted cosmetic changes (issuing black berets to all regular troops, for example) and fought against some substantial innovations (developing an armored vehicle on wheels and not treads), General Keane said he expected no resistance if the Army deploys forces outside the traditional echelons of divisions or brigades.

For example, he said, the Army is poised, if required, to assign to an Air Force officer the command of Army air defense units or Apache attack helicopters if that would assist in carrying out a mission.

The Army already demonstrated such flexibility in Iraq, he said, when many conventional Army troops and marines were assigned to Special Operations commanders.

General Keane, a gregarious former New Yorker, was sought by Mr. Rumsfeld to replace Gen. Eric K. Shinseki, the Army chief with whom the secretary clashed over weapons procurement and troop strength for postwar Iraq. General Keane declined the offer because of family commitments, and a new Army chief, Gen. Peter J. Schoomaker, was sworn in on Friday.

Asked about reports of tension between Mr. Rumsfeld and the Army, especially arguments as to whether sufficient troops were assigned to Iraq, General Keane said such questions were an overstatement. He then answered with a commentary that deftly combined standard Army doctrine and Mr. Rumsfeld's own view of how to transform the military into a more agile and lethal force.

"Combat power will always have a quality of mass that's associated with it and a quality of numbers," he said. "I'm not suggesting it doesn't. All I am suggesting is that some people focus on that so narrowly that they add up the number of Iraqi divisions, for example, that we were attacking, and they add up the number that we were attacking with, and they see an imbalance."

Some military analysts, he said, miss the point.

"They don't recognize that we have a significant overmatch in leadership, skill and will," General Keane said. "And that if you achieve tactical surprise, and if you attack in three locations at the same time, that is going to have dramatic impact on that enemy. And if you integrate all of the combat power, not just the ground combat power, at the same time, that will have significant impact on the enemy."

General Schoomaker and General Keane have both said in public statements that the Army probably needs more troops to meet its global commitments. "There is no doubt," General Keane said today, noting that the Army is short of infantry, military police and chemical-biological warfare units.

But he said that before the Army asked for more troops, it hoped to examine two issues: whether it can shift some jobs performed by military personnel to civilians and whether the strain on the National Guard and reserves could be eased if tasks required early in a conflict but now performed by reservists could be assigned to active-duty troops.

At the Pentagon today, Mr. Rumsfeld said he was open to analyzing whether the military needed to grow, but he said that thus far he had not seen convincing evidence to make the case for more troops.

He said many steps should be taken before asking Congress for money to increase the size of the military, among them cutting back on less urgent foreign missions, transferring people in uniform out of administrative tasks and back to combat units and using more Iraqis and foreign troops for the mission in Iraq.