IN dinner conversations for months, the subject that inevitably came up was O.J. Simpson. Then, for a few days, it was Cal Ripkin. Lately it has been overwhelmingly Colin Powell. And no wonder! The publication of General Powell's memoirs, ''My American Journey,'' has been greeted with a wave of publicity such as I have never witnessed - a wave in which he zestfully bathes. In his interviews, he runs a gamut from aw, shucks, just an ordinary kid from the South Bronx, to a self-confident leader who believes he has what it takes to inspire America. ''I'm tanned, rested, and ready - ha, ha,'' he said to one group of admirers at a Time magazine reception. He seems fully aware that the nation hangs on every teasing word that may betray his intentions. Will he run or won't he? And if he does, on what ticket? Tantalizingly, he suggests it could be Republican, maybe independent, perhaps even Democratic, just to be all-inclusive. The pundits predicted that he would avoid taking positions on issues. They were wrong. He took unambiguous positions on issues - pro-choice, pro-registration of guns, pro-affirmative action, pro-death penalty. If Powell has not proved himself as a political leader, he has certainly proved himself as a political performer. Movie lobbyist Jack Valenti, one-time Lyndon Johnson aide, told him admiringly, ''If you run for president, you'll be formidable. And if you don't, you'll be rich.'' Formidable is the way the media have thrown skepticism to the winds to worship at the Powell shrine. ''Powell Mania,'' the Washington Post calls it. ''Can Colin Powell Save America?'' trumpets the cover of Newsweek. ''He would make a good president and it would be good for the country,'' says ABC's usually abrasive Sam Donaldson. Only now and then do you get questions about how Powell handled - or didn't handle - the My Lai massacre in Vietnam. Or whether he was too quick to call off the war against Iraq. For the rest, the media are acting the way much of the American public is acting - so hungry for someone fresh in politics as to suspend disbelief and join a sort of national revival meeting. No one knows better than Colin Powell how fast a balloon can be deflated. So, he troops in and out of TV studios, but he doesn't inhale the adulation. He is still the risk-averse military planner who wants to know where the battle will end before he commits his forces. But Powell-mania sells books, and he rides the wave like a skilled surfer. My impression of the book and the first spate of interviews is that Powell has effectively eliminated himself from the traditional party system. He has turned his back on the Democratic Party (''They're not alive and well like the Republican Party is'') and he has virtually ensured that the Republicans will turn their back on him. His positions on abortion rights, affirmative action, and gun control make him anathema to the right wing that today controls the GOP. The Powell phenomenon underlines the disconnect between what it takes to win a nomination and what it takes to win an election. Party activists control the nomination, which is why we occasionally get losing candidates like William Jennings Bryan, Barry Goldwater, and George McGovern. There are Republicans alive today who still think the 1952 nomination should have gone to Sen. Robert Taft rather than Gen. Dwight D. Eisenhower. The party faithful want an ideologically correct candidate more than they want a winning candidate. That leaves General Powell, if he is so minded, to undertake the almost impossible task of running as an independent.