WASHINGTON - The Pentagon on Thursday proposed increasing the size of the Army and Marine Corps by a combined total of 92,000 troops and announced it will recall to duty sooner than planned some National Guard and Reserve troops who already have served yearlong tours in Iraq or Afghanistan.

At a news conference, Defense Secretary Robert Gates also announced that "from this point forward," the amount of time that Guard and Reserve units will be mobilized for federal duty will be limited to 12 months. Until now, mobilizations have ranged from 16 to 24 months, although time inside Iraq is usually limited to 12 months.

Separately, as part of President Bush"s plan for boosting U.S. troop strength in Iraq, a brigade of National Guard soldiers from Minnesota will have its yearlong tour in Iraq extended by 125 days, to July, and a Patriot missile battalion will be sent to the Persian Gulf next month, according to a defense official who spoke on condition of anonymity.

Maj. Randy Taylor, a spokesman for the 3rd Battalion, 43rd Air Defense Artillery Regiment, at Fort Bliss, Texas, said that Patriot unit has been ordered to deploy to the Gulf region but he would not identify the specific country or the specific date in February, citing security concerns. He was unable to say how many soldiers will deploy with the Patriot missiles. The last time the unit deployed to the Gulf was in 2003, Taylor said.

The Marines announced that two infantry units — the 3rd Battalion, 4th Marine Regiment, and the 1st Battalion, 6th Marine Regiment — will stay in Iraq 60 to 90 days longer than scheduled. That will enable the Marines to have a total of eight infantry battalions in western Anbar province instead of the current six, by February. Once the 60 to 90 day extension is over, another two battalions will be sent in early from their U.S. bases.

Also, the 15th Marine Expeditionary Unit, which combines infantry with a helicopter squadron and a logistics battalion, totaling about 2,200 Marines, will stay in Anbar for another 45 days.

Those extensions conform with Bush"s announcement Wednesday evening that he was ordering 4,000 more Marines to Anbar.

The military tries to avoid extending combat tours and sending forces earlier than planned because it disrupts the lives of troops and their families and makes it harder for the services to get all troops through the education and training programs they need for promotions. But in this case it was deemed unavoidable.

Richard Myers, the retired Air Force general who was chairman of the Joint Chiefs of Staff when the Iraq war began, said in a telephone interview that he believes Bush"s decision to add 20,000 troops in Iraq was based on calculations by military commanders on how many extra troops are needed to accomplish their mission.

"The key is: Can the prime minister deliver on those things he has promised to deliver on," Myers said, referring to Nouri al-Maliki"s pledge not to shield Shiite militias from raids by Iraqi and American forces.

Gates said the "planning objective" for the Guard and the Reserve will remain five years between each mobilization, but because of the demands of war an undisclosed number of units will be called up more frequently. "Our intention is that such exceptions be temporary," Gates said. He did not say which units would be remobilized.

An internal Army document obtained by The Associated Press on Thursday said that without more frequent use of Guard and Reserve forces through remobilization of units that already have served in Iraq, "we will break" the active-duty Army.

Appearing with Gates at the news conference, Gen. Peter Pace, chairman of the Joint Chiefs of Staff, told reporters that the decision to recall Guard and Reserve units was contemplated even before Bush decided to increase U.S. forces in Iraq. Even at the existing level of forces in Iraq, the Army was unable to sustain for much longer its troop rotations with the active-duty force alone.

Speaking just hours after Bush announced that 21,500 more troops will be sent to Iraq in coming months, Gates said he was recommending to Bush that the Army"s troop strength be increased by 65,000 soldiers, to a total of 547,000 worldwide. Almost half of that increase already has been achieved under a temporary program that Gates said would be made permanent; the full increase is to be achieved within five years.

The Marine Corps, the smallest of the military services, would increase over five years by 27,000 — to 202,000. The increase would be from a base of 175,000, although the Marine actually have 179,000 in uniform now, according to Brig. Gen. Robert Milstead, the chief of Marine Corps public affairs at the Pentagon.

The cost of these service increases will be enormous. The Army estimates that each additional 10,000 soldiers costs it about $1.2 billion a year. Expanding the Army and Marine Corps, which have been strained by the wars in Iraq and Afghanistan, also will put more demands on their recruiting services, which have struggled in recent years to attract people during time of war.