WASHINGTON – It could be a long weekend for thousands of former soldiers.

The Army says it will begin notifying more than 5,600 of those soldiers next week that they are being involuntarily recalled to active duty and could be sent to Iraq or Afghanistan as early as this fall.

In Maine, Sen. Susan Collins said she received confirmation from the Department of Defense that 51 Mainers are expected to be recalled to active duty for possible service in Iraq or Afghanistan. Seven other Mainers may be called at a later date, she said.

Collins, a member of the Senate Armed Services Committee, said Wednesday that the “fact that the Individual Ready Reserve is now being called upon is further evidence that we have overtaxed our Guard and Reserve troops.” Collins said that is why she voted “to increase the end strength of active duty Army personnel – meaning full-time troops – by 20,000.”

Sen. Olympia Snowe, who also voted to increase active duty forces, said Wednesday, “I remain resolute that reinstating the draft is not a solution … It is also time for our allies, particularly under the NATO flag, to increase their military participation in combating the global war on terror.”

“There’s going to be soldiers who, yes, will be shocked,” said Col. Debra A. Cook, commander of the Army’s Human Resources Command and the final arbiter of petitions for exemption.

Most of the former soldiers recently left the Army as truck drivers, mechanics, supply clerks, administrative clerks or combat engineers. All will be kept on active duty for at least 18 months but not longer than two years. The first formal notifications are due to arrive in mailboxes on Tuesday.

The call-up will be done in three increments from July to December.

It is the first large-scale use of former soldiers in the Individual Ready Reserve since 1991. But it is not the first time the Army has dipped into this category of reserves for Iraq.

Defense Secretary Donald H. Rumsfeld authorized the Army to do so in January. As a result, small numbers of former soldiers have been called up, with little or no publicity.

Tom Bunch of Chillicothe, Ohio, said in a telephone interview Wednesday that his 29-year-old son Jon of Madison, Wis., was called up from the IRR in April and is due to fly to the Gulf on Friday.

The younger Bunch was an active-duty artillery officer in 1998-99 and then spent three years in the National Guard. The Army contacted him early this year about transferring from the IRR to the National Guard or Reserve where, it was implied, he would be less likely to wind up in Iraq.

“He thought he’d take his chances,” so he stayed in the IRR where his military commitment was due to expire next June, the elder Bunch said. “He didn’t know if they were blowing smoke.”

Members of Congress were informed Tuesday of what the Army called a “potentially emotional and historic” decision to reach deeper into the Individual Ready Reserve.

Some leading Democrats cited it as evidence that the Bush administration had underestimated the length of time and number of American troops it would take to stabilize and rebuild postwar Iraq.

Rep. Ike Skelton, D-Mo., the ranking Democrat on the House Armed Services Committee, said the mobilization was “a clear signal that we need to provide more troops to the overburdened U.S. Army.” Skelton has led a push to increase the size of the active-duty Army, which Congress has mandated at 482,400.