WASHINGTON - The Pentagon will adopt a new strategy that for the first time orders the military to anticipate that future conflicts will include a complex mix of conventional, set-piece battles and campaigns against shadowy insurgents and terrorists, according to senior officials.

In officially embracing hybrid warfare, the Pentagon would be replacing a second pillar of long-term planning. Senior officials disclosed in March that the review was likely to reject a historic premise of American strategy - that the nation need only to prepare to fight two major wars at a time.