ByJohn S. McClenahen Having discontinued development of its Sonic Cruiser, a near-supersonic commercial aircraft, Chicago-based Boeing Co. is now concentrating development efforts on a new high-efficiency 200- to 250-seat airplane designated the 7E7. The new plane is expected to use many of the technologies developed for the Sonic Cruiser. Overall leader of the development effort will be Michael B. Blair, most recently the head of Boeing's commercial aviation services business and a veteran of the 777 jet transport program. Walter B. Gillette will be responsible for aircraft development, including engineering and manufacturing. John N. Feren will head up sales, marketing and service support. Craig A. Saddler will lead the finance and business operations of the 7E7 program. Boeing figures the market potential for the 7E7 is as many as 3,000 aircraft during the next 20 years. Boeing expects to offer the plane to customers next year and foresees it going into commercial service in 2008.