WASHINGTON, Oct. 17 — American intelligence officials have concluded that Pakistan, a vital ally since last year's terrorist attacks, was a major supplier of critical equipment for North Korea's newly revealed clandestine nuclear weapons program, current and former senior American officials said today. The equipment, which may include gas centrifuges used to create weapons-grade uranium, appears to have been part of a barter deal beginning in the late 1990's in which North Korea supplied Pakistan with missiles it could use to counter India's nuclear arsenal, the officials said. "What you have here," said one official familiar with the intelligence, "is...