W A S H I N G T O N, Dec. 10 — The United States possibly could have prevented the Sept. 11 hijackings if intelligence agencies had reported to a single leader, with the resources to link scattered clues, a senator investigating the attacks says. Sen. Bob Graham, outgoing chairman of the Senate Intelligence Committee, said Monday that lawmakers hope to prevent future attacks by recommending creation of a national intelligence director, a Cabinet-level post that would oversee all U.S. intelligence operations. It is a principal recommendation of an inquiry into the attacks by the House and Senate intelligence...