Small remotely piloted planes are now used mainly to gather intelligence and fire missiles at insurgents. But over the next several decades, the Air Force envisions building larger ones that could do the work of bombers and cargo planes and even tiny ones that could spy inside a room. In a report released Thursday laying out a flight plan for developing pilotless systems, the Air Force also said it could eventually field swarms of drones to attack enemy targets. And it will have to be ready to defend against the same threat, which could become another inexpensive way for insurgents to attack American forces. Col. Eric Mathewson, who directs the Air Force task force on pilotless aerial systems, said in an interview that the service sketched its vision to encourage contractors and university researchers to help create the technologies. Military contractors have already been rushing to expand in what promises to remain a prime growth area even as Pentagon budgets tighten. In the last decade, the use of remotely piloted planes has soared in Iraq, Afghanistan and Pakistan. The Air Force and the Central Intelligence Agency have fielded Cessna-size drones, called Predators and Reapers, to send back video of insurgent activity and mount missile attacks. Army units have used hand-launched models, which look like toy planes, to peer over hills or buildings. Other drones monitor the seas and eavesdrop from high altitudes, much like the storied U-2 spy planes. But many of the systems have been rushed out in an almost reactive fashion, Colonel Mathewson said. At the same time, we have put industry and academia at a disadvantage because we havent told them where were going, he said. So we wanted to describe the future, so they could help us find the solutions. Colonel Mathewson said the goal was to create economical alternatives for most Air Force missions. In that sense, the plan which was approved by Air Force Secretary Michael B. Donley and Gen. Norton A. Schwartz, the Air Force chief of staff helps cement a major cultural change at the service, where many pilots initially recoiled at the idea of drones. Colonel Mathewson said the service would like to create modular craft basic airframes that could be easily configured for different missions. The report envisions a family ranging from nano-size drones that could flit inside buildings like moths to gather intelligence, to large aircraft that could be used as strategic bombers or aerial refueling tankers. Midsize drones could act like jet fighters, attacking other planes or ground targets and jamming enemy communications. The changes will begin with enhancements of current systems, Colonel Mathewson said. The more exotic changes would come from 2020 through the 2040s. Perhaps the most controversial is the idea of drones swarming on attack. Advances in computing power could enable them to mount preprogrammed attacks on their own, though that would be a difficult legal and ethical barrier for the military to cross. But before long, even a single insurgent could dispatch several small drones at once. Referring to the improvised explosive devices that insurgents have planted like mines in Iraq and Afghanistan, the report warned that the next inexpensive threat to American troops could be an airborne I.E.D.