The government began providing Secret Service protection for Democratic presidential candidate the Rev. Jesse Jackson, whose campaign complained last week of threats by the Ku Klux Klan. Another presidential candidate, George Bush, is guarded by Secret Service agents because he is vice president. Former television evangelist Pat Robertson, citing threats against him, has asked for Secret Service protection but officials said there has been no decision on the request. Other candidates will receive Secret Service protection beginning in January. A Jackson campaign spokesman said seven agents would protect Jackson around the clock, with the exception of his Thanksgiving trip to the Persian Gulf.