ASHINGTON, June 29 — Amid Congressional concerns that the military is stretched too thin, the Army is preparing to take advantage of a rarely used wartime program that allows it to recall soldiers who have left the service and did not join the reserves. Pentagon officials said Tuesday that 5,600 former soldiers were going to be called up for yearlong tours, mostly assignments in Iraq and Afghanistan.

The decision was immediately cited by members of Congress as more evidence that the deployments to Iraq and Afghanistan and, more broadly, for the global campaign against terrorism, have left the Army unable to fulfill all its missions. Likewise, the presidential campaign of Senator John Kerry quickly issued a statement Tuesday labeling the decision troubling news.

Proposals to expand the Army already are being debated in Congress, where some lawmakers have described the large reserve mobilizations and other unusual steps to fill the rosters in Iraq and Afghanistan as an unofficial draft.

Pentagon and military officials have resisted calls to increase the size of the Army, saying they would rather find efficiencies elsewhere in the service first. They also warn that decisions to expand the Army would lock the Pentagon into expensive personnel budgets for years to come.

The nation's pool of former officers and soldiers who are subject to being recalled to service is known as the Individual Ready Reserve. It allows the military to select specialists with needed skills, and it has not been used in such large numbers since the Persian Gulf war of 1991.

"Remember, we are at war," said a Pentagon official who confirmed the Army's plan to mobilize 5,600 members of the ready reserve.

Most of those called up will perform support and logistical jobs like truck drivers, mechanics, administrative specialists, food service workers and engineers. One Pentagon official said that the military police would also be included.

Members of Congress have been briefed this week on the Army's plans. Defense Secretary Donald H. Rumsfeld gave the Army broad authority in January to reach into the Individual Ready Reserve, although the specifics of the new call-up were approved only in recent days.

The decision follows an announcement early this month that the Army would require all soldiers bound for Iraq and Afghanistan to extend their active duty at least until their units return home from their missions there, a move that could keep thousands of troops in the service for months longer than they expected.

That announcement, called "stop-loss, stop-move," expanded an existing program that applies to many troops already in the two countries, and means that soldiers who had planned to retire, move to other Army jobs or leave the military when their enlistments expired will be required to stay for the length of their units' deployment in either of the two combat zones.

There are about 140,000 American troops now in Iraq and about 20,000 in Afghanistan.

The Pentagon also is already relying heavily on the regular reserve component. In addition to the active-duty force, the Pentagon as of June 16 had brought on to service 136,460 members of the Army Reserve and National Guard, people who voluntarily signed up to be on call and who generally have spent a weekend a month and two weeks a year in training.

In contrast, the 117,000 names in the Individual Ready Reserve have not been associated with the armed services since their departure from the Army — except to register their location — and have not been training with a unit.

The new ready reserve decision does not apply to the other services, said a Pentagon official who also said that the Army first would look to members of the ready reserve who recently left the service.

The Individual Ready Reserve is made up of soldiers who were honorably discharged but served less than eight years on active duty and still have obligations under the contract signed when first joining the service.

On Capitol Hill this month, the Senate voted overwhelmingly to increase the strength of the Army by 20,000 soldiers. Members of both parties said the troops, added to the Pentagon spending plan for 2005 on a 93-to-4 vote, were essential in light of international tensions and the policy of keeping military personnel in Iraq and elsewhere beyond their scheduled tours.

Senator Jack Reed, Democrat of Rhode Island and a chief proponent of more troops, issued a statement Tuesday that said: "This is another indication of the urgent need to increase the size of the Army. The administration's assessment of the number of troops needed to occupy Iraq, fight the war on terror and maintain the nation's military commitment around the world has been woefully inadequate."

Mr. Reed has been joined by senior Republicans, including Senators John McCain of Arizona and Chuck Hagel of Nebraska, in pressing for a personnel increase as well as for dispatching more forces to Iraq. The House also has approved legislation calling for additional troops.

Gen. Peter J. Schoomaker, the Army chief of staff, said earlier this month that he would have no hesitation in requesting more troops if the current level of stress on the force is continued in future years and the required combat strength cannot be found elsewhere in the Army.

But he noted that personnel costs are the largest share of his budget, and he warned against expensive decisions now that may not be as relevant in future years.

After word of the ready reserve mobilization began circulating, the Kerry campaign issued a statement Tuesday saying that the decision was evidence of a failed Bush administration foreign policy in Iraq.

"The fact is that this involuntary call-up is a direct result of the Bush administration's diplomatic failure to get real international help in Iraq," said Rand Beers, Mr. Kerry's adviser on national security issues.