(FORTUNE Magazine) – Growing up in Boise, Idaho, Frank Shrontz would sometimes appear in one brown and one black shoe. ''His concentration was amazing, so sometimes he was oblivious to everything else,'' says longtime friend Harry Turner, an Idaho lawyer. Concentration is a quality Shrontz, 55, will need in abundance as he helps Boeing cope with the problems of preeminence. With 1986 sales of $16.3 billion, it is the world's largest maker of aircraft. It is also one of the U.S.'s most important defense contractors. But rising cost-consciousness at the Pentagon and a temporary downturn in 747 deliveries will thin Boeing's profits in 1987. A lawyer with a Harvard MBA, Shrontz joined Boeing in 1958 and made his mark mastering the arcana of aircraft contract administration. That served him well between 1973 and 1977, when he worked as an assistant secretary of the Air Force and later of defense. After leaving the Pentagon, Shrontz briefly considered joining General Dynamics. But his love of the West impelled him back to Seattle-based Boeing. During the energy crisis of the late 1970s, he championed the mid-range 737 over the more fuel-efficient and longer-range 757 and 767. The move was either lucky or prescient. When oil prices collapsed and federal deregulation encouraged short-hop flights, the 737 became Boeing's biggest seller. Shrontz was named president in 1985 and chief executive a year later. His predecessor, Thornton Wilson, who remains chairman, is a blunt-spoken engineer. Shrontz is better known for lawyerly logic. One of the few impulsive acts of his life occurred in 1953. Then a college junior, he spied a pretty girl on campus and declared he was going to marry her. Shrontz and the former Harriet Houghton recently celebrated their 33rd wedding anniversary.