WASHINGTON - The Pentagon has abandoned its limit on the time a citizen-soldier can be required to serve on active duty, officials said yesterday, a major change that reflects an Army stretched by longer-than-expected combat in Iraq.

Gen. Peter Pace, chairman of the Joint Chiefs of Staff, said yesterday that the change would have been made even if Bush had not ordered an additional 21,500 troops to Iraq.

The Pentagon also announced that it was proposing to Congress that the size of the Army be increased by 65,000, to 547,000, and that the Marine Corps, the smallest of the services, grow by 27,000, to 202,000, over the next five years. No cost estimate was provided; officials said it would be at least several billion dollars.

Until now, the Pentagon's policy on the Guard or Reserve was that members' cumulative time on active duty for the Iraq or Afghan wars could not exceed 24 months. That cumulative limit is now lifted; the remaining limit is on the length of any single mobilization, which may not exceed 24 consecutive months, Pace said.

In other words, a citizen-soldier could be mobilized for a 24-month stretch in Iraq or Afghanistan, then demobilized and allowed to return to civilian life, only to be mobilized a second time for as much as another 24 months. In practice, Pace said, the Pentagon intends to limit all future mobilizations to 12 months.

Members of the Guard combat brigades that have served in Iraq in recent years spent 18 months on active duty - about six months in pre-deployment training in the United States, followed by about 12 months in Iraq. Under the old policy they could not be sent back to Iraq because their cumulative time on active duty would exceed 24 months. Now that cumulative limit has been lifted, giving the Pentagon more flexibility.

The new approach, Pace said, is to squeeze the training, deployment and demobilization into a maximum of 12 months. He called that a "significant planning factor" for Guard and Reserve members and their families.

A senior U.S. military official who briefed reporters yesterday on Iraq-related developments said that by next January, the Pentagon "probably will call again" on National Guard combat brigades that previously served yearlong tours in Iraq.

Defense Secretary Robert Gates, appearing with Pace, said that although the Pentagon's goal was to mobilize Guard and Reserve units no more frequently than one year out of six, the demands of wartime will require it to call up some units more often than that. He provided no details on how many units would be remobilized at the faster pace.