Former presidential contender Jesse Jackson will no longer be giving away his spellbinding oratory. He's going for the big money and has signed with the Agency for Performing Arts with a $1 million advance for personal and television appearances and writing books. At $25,000 a speech, he's in the big leagues with former secretaries of state Henry A. Kissinger and Alexander M. Haig Jr. and columnist Art Buchwald . . . Noted authors Howard Fast ("The Last Frontier" and "Citizen Tom Paine") and Stephen Birmingham ("Our Crowd" and "The Grand Days: America's Sephardic Elite") are the guest speakers Sunday at the second annual Jewish Book Fair at the Jewish Community Center in Rockville. Fast's newest book is "The Outsider"; Birmingham's is "The Rest of Us" . . . How tough can you be in an argument with your boss? Frank Mankiewicz, a well-credentialed Democrat working as an executive vice president at Gray & Co., will debate his boss, Robert Keith Gray, a man with sparkling Republican credentials, on the topic "Reagan versus Mondale" today at a luncheon of the Washington Society of Investment Analysts in the Sheraton-Carlton hotel . . . It may be the only landslide victory Walter Mondale will get this year. On Tuesday a streetcorner poll was held at the Connecticut Connection at Connecticut and L and 2,928 passersby participated, mostly from D.C., Maryland and Virginia, with 10 percent from other areas. Mondale won 60 percent of the vote. Those from other areas, incidentally, cast 60 percent for President Reagan . . . Mort Sahl, the satirical dark prince of the 1960s, opened this week at Charlie's Georgetown and hasn't lost his sharpness. He described CIA director William Casey as "the spy who came in for the gold," and said President Reagan left before the movie "Country" was over. "When the bank foreclosed he thought that was the happy ending."