Douglas Kiker, 61, an NBC correspondent and veteran political reporter, died yesterday in his sleep, apparently of a heart attack, at his summer home in Chatham on Massachusetts' Cape Cod. He had been with the network since 1966 and most recently was a contributor to "NBC Nightly News." President Bush, in a handwritten note of condolence to an NBC reporter, said, "I respected Doug -- so did all who saw him as the fair, objective and decent man he was. I'm sorry you've lost a good friend." Before he joined NBC, Mr. Kiker was the White House correspondent for the New York Herald Tribune and was in the presidential motorcade when President John F. Kennedy was assassinated in Dallas in 1963. A native of Griffin, Ga., he served in the Navy during the Korean War and started his reporting career on the Atlanta Journal. He wrote several novels, in.