The Senate began debate on the nomination of Robert M. Gates to become director of the Central Intelligence Agency. The Senate vote will take place November 6, ending more than four months of Senate examination of Mr. Gates' qualifications for the post. Although it now appears that Mr. Gates will be confirmed by the full Senate, his nomination hit some rough spots earlier as members of the Intelligence Committee probed his involvement in the 1986 Iran-Contra scandal. CIA analysts had charged that during earlier employment with the CIA Gates had revised intelligence estimates to conform with the policy objectives of the Reagan administration.