WASHINGTON — The Pentagon’s decision to cut the size of the Army by 80,000 soldiers will force the military to rely more on the National Guard and reserves, particularly if the U.S. gets into two major, long-term combat operations at the same time, according to the top Army officer.

Gen. Raymond Odierno, chief of staff of the Army, said this morning he is comfortable with the mandate to go from 570,000 soldiers during the height of the Iraq war to 490,000 by 2017.

But he suggested that the U.S. will now have to keep its reserve forces at a higher level of readiness than it did before the wars in Iraq and Afghanistan pressed tens of thousands citizen soldiers into service to buttress the active duty Army.

He also said his support for the force cuts hinges on the fact that the Army will have five more years to make the reductions, largely through normal attrition. He acknowledged, however, that a small number of officers may have to be forced to leave.

If the military had to fight two large, simultaneous, long-term wars, he said, the U.S. would rely more heavily on its allies in the region and call for a massive mobilization of the reserves.