CHANCES are that by the time Sen. Edward Kennedy comes up for reelection in 1994, his nephew's Palm Beach rape trial will have become a vague memory in the public's mind.But that hasn't dampened the media's enthusiasm for speculation about this episode's impact on a political career that has spanned 29 years and made Senator Kennedy one of the most powerful legislators on Capitol Hill. There is the oft-cited Boston Herald poll of Aug. 1 that pitted Kennedy against Massachusetts' Republican Gov. William Weld in a hypothetical race and showed him losing by 55 to 32 percent. And there are the numerous liberal Boston columnists and Boston Globe editorials that have suggested it may be time for Kennedy to reassess his future. But Kennedy supporters aren't worried. Michael Goldman, a Massachusetts Democratic consultant who has worked for another Kennedy nephew, Rep. Joseph Kennedy II, says his polling data indicate that whenever the trial fades from the news, the senator's ratings rebound. More important Mr. Goldman says, is how voters vote. "They ask themselves, 'Does he care about people like me? Has he done anything for me?' I predict he will win, and fairly convincingly." It is not the senator who is on trial in Palm Beach - though some have mused, including defendant William Kennedy Smith himself, that this is really a trial of the whole family. Rather, Teddy Kennedy is seen as having failed as the father-surrogate who led his nephew astray by taking him on the late-night outing that led to the rape charge. Furthermore, this episode has triggered a public revisiting of the senator's private life, from Chappaquiddick to the present. In October he surprised listeners with a speech at Harvard acknowledging his "shortcomings." Massachusetts Republicans, emboldened after retaking the State House, smell blood, and aren't terribly inclined to dampen speculation that Kennedy may be in trouble. "There's a new generation of voters now that doesn't consider the Kennedys as saints, that didn't grow up with the Camelot myth," says Todd Domke, a Massachusetts Republican consultant. "His invincibility is gone."