In a new sign of mounting strain from the war in Iraq, the Army has extended the combat tours of about 4,000 soldiers who would otherwise be returning home, defense officials said Monday.

The 1st Brigade of 1st Armored Division, which is operating in the vicinity of Ramadi, the capital of Anbar province, will be kept in place for several weeks beyond its scheduled departure, the officials said. The officials spoke only on condition of anonymity because the decision has not been formally announced by the Pentagon.

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Also, Defense Secretary Donald H. Rumsfeld told reporters that "some units" are being sent to Iraq ahead of schedule, although he offered no details. Rumsfeld declined to discuss the case of the 1st Brigade, 1st Armored, saying that as a general matter some units, "from time to time," are extended in Iraq.

The brigade's home base is in Germany. The soldiers' families were notified on Monday that instead of going home in early January as scheduled, the brigade would be kept in Iraq until February — an extension of about six weeks, one of the officials said. Army officials also have notified members of Congress.

The brigade has about 4,000 soldiers in Iraq. They are not the first to be extended.

In late July the Army extended the Iraq tour of the Alaska-based 172nd Stryker Brigade. About 300 soldiers from that unit had already returned home and were required to go back to Iraq. The brigade is now operating in Baghdad.

The reasons for these extensions are different, but they both reflect the fact that the Army is hard pressed now to maintain rotations for Iraq and Afghanistan at the current pace. The 172nd was extended by four months in order to strengthen U.S. forces in Baghdad, where commanders are trying to avert a full-scale civil war.

The 1st Brigade of the 1st Armored Division was extended in order to allow its replacement unit, the 1st Brigade of the 3rd Infantry Division, a minimum 12 months between overseas tours, the official said. The 3rd Infantry has already served two tours in Iraq, including the initial invasion of the country in March 2003.

Last week, the top American commander in the region said the U.S. military is likely to maintain and may even increase its force of more than 140,000 troops in Iraq through next spring. Gen. John Abizaid, commander of the U.S. Central Command, said military leaders would consider adding troops or extending the Iraq deployments of other units if needed.

Until sectarian violence spiked early this year, Bush administration officials had voiced hopes that this election year would see significant U.S. troop reductions in what has become a widely unpopular war.

The Army has a stated goal of giving active-duty soldiers two years at home between overseas combat tours, but it is unable to achieve that "dwell time," as the Army calls, because it does not have enough brigades to meet the demands of simultaneous wars in Iraq and Afghanistan. It would not be a problem now if the situation in Iraq had improved enough to allow the Army to reduce its presence as originally planned.

Army Secretary Francis Harvey told The Associated Press last week that the amount of time between deployments has shrunk this year from 18 months to 14 months. In the case of the 3rd Infantry, it appears at least one brigade will get only about 12 months because it is heading for Iraq to replace the extended brigade of the 1st Armored.