WASHINGTON -- As security improves in Iraq, pressure is building to reverse one of the most onerous decisions Defense Secretary Robert Gates made to enable President Bush's troop buildup to go forward this year: extending the tours of active-duty soldiers from 12 months to 15 months.

The extra three months is a weighty burden, both physically and psychologically, for soldiers already stressed by multiple tours, and on families coping with strains that have mounted since the war began in 2003.

"We can't sustain that," Gen. George Casey, who was the top U.S. commander in Iraq before becoming the Army chief of staff at the Pentagon in April, said recently. "We have to come off that." He said a decision on cutting tour lengths could be announced in three or four months.

Army leaders are pushing to shorten tour lengths back to 12 months by summer, when Bush's troop buildup is scheduled to end. But senior commanders in Baghdad appear reluctant to commit to a change until perhaps late next year, fearing that Iraqi stability still will be in doubt until that point.

The outcome depends in large part on what Bush decides to do next spring after hearing an updated assessment of Iraq from his top commander in the country, Gen. David Petraeus. At hand then will be a decision on whether to continue cutting U.S. troops levels beyond July. If no further cuts are made, it will be much harder for the Army to back away from the 15-month tours.

There are now 166,000 U.S. troops in Iraq, about 30,000 more than when Bush announced his buildup last January. By July that is supposed to have fallen back to about 135,000. Although Bush has not committed yet to going lower, Gates has expressed hope it could drop to 100,000 by next December.

At least 3,886 members of the U.S. military have died in the war since it started, although casualties have slowed.

On a visit to Iraq this past week, Gates said he was encouraged by security gains but cautious about future progress.

As a measure of Army leaders' concern about excessively long tours, the vice chief of staff, Gen. Richard Cody, told soldiers in February -- two months before the decision on 15-month tours was made -- that the prevailing standard of 12 months was too long. Cody said the goal was to cut it to nine months.

Among the soldiers hit hardest by the extended tours are those in certain units of the 1st Cavalry Division. They deployed to Iraq from Fort Hood, Texas, last fall with orders to return within 12 months. Then came the word in April that everyone would stay for 15 months.

The 15-month standard does not apply to Army National Guard or Army Reserve soldiers. Marines generally serve seven-month tours, although they get less time between tours than do soldiers.