I believe it was William Safire:
http://www.bartleby.com/73/1553.html
We might both be right, although I was watching McLaughlin awhile back when he claimed Pat wrote it and the Irishman just smiled.
"With the help of White House speechwriters Pat Buchanan and William Safire, Agnew developed a distinctive, jeering speech style that mixed some heavy fun into the contempt.
In a 1969 speech against war protesters, he said, "A spirit of national masochism prevails, encouraged by an effete corps of impudent snobs who characterize themselves as intellectuals." "In the United States today," Agnew told a 1970 audience in San Diego, "we have more than our share of the nattering nabobs of negativism." He went after "pusillanimous pussyfooters" and "vicars of vacillation" and "the hopeless, hysterical hypochondriacs of history."
http://www.time.com/time/magazine/article/0,9171,985217,00.html
"Pat worked as an advisor and speechwriter for Richard Nixon and was the author of Spiro Agnew's famous "nattering nabobs of negativism" phrase."
http://www.fuldaohio.com/famous_fulda_faces.htm
"In the modern era, then Vice President Spiro Agnew kicked off the modern era of political pandering with a speech he delivered in Des Moines, Iowa in 1969, written partially by Pat Buchanan. In that speech, Agnew went after "the media," and exploited small town and rural folks' insecurities and suspicion of Easterners and the well-educated in order to deflect attacks on the Presidents' policies. It was in that speech that we were introduced to academics as "an effete corps of impudent snobs." Later, Agnew would regale us with "nattering nabobs of negativism." The message? Hate people who know more than you!"
http://www.gapersblock.com/airbags/archives/pandering_pandering_pandering/