WASHINGTON -- The Pentagon has announced that all active-duty Army soldiers in Iraq and Afghanistan will serve three months longer than expected.

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"This policy is a difficult but necessary interim step," Secretary of Defense Robert Gates told a Pentagon news conference.

It applies to all active-duty Army units with the exception of two brigades currently in Iraq that have already been extended to 16 months. Marine Corps, Navy and Air Force units serving in Central Command and Army National Guard and Army Reserve units deployed to the are not affected.

It's one of a series of Pentagon maneuvers to cope with the strains of fighting wars in Iraq and Afghanistan while maintaining a higher troop level in Iraq, Gates said.

The new policy also seeks to ensure that all active-duty Army units get at least 12 months at home between deployments, Gates said.

It would also allow the Pentagon to maintain the current level of troops in Iraq for another year, although Gates added that there has been no decision on future troop levels.

"Without this action, we would have had to deploy five Army active-duty brigades sooner than the 12-month at-home goal," Gates said. "I believe it is fairer to all soldiers that all share the burden equally."

"I realize this decision will ask a lot of our Army troops and their families," he said.

On Monday, officials announced 13,000 National Guard troops would be getting orders alerting them to get ready for possible Iraq deployment later this year.

In related news, The Associated Press reported that, after four years of war, the campaign to entice Army soldiers and Marines to stay in the military has passed the $1 billion mark.

That's what was spent on re-enlistment payments last year, compared with $174 million in 2003, when the war started.

Bonuses can range from a few thousand dollars to $150,000 for very senior special forces soldiers who re-up for six years.

All service branches met or exceeded their active-duty recruiting goals in March, but three of the six reserve components missed their targets, Defense Department officials said on Tuesday.