FOR the office of US president, all but one person every four years lose. Loss for challengers in '92 approaches dead certainty. Is it better to run and lose than not to have run at all?The elixir of presidential ambition does not clear the head. Once it is downed and a candidate is committed to running, there may be no graceful exit. An embarrassing slip or fundraising impotence takes a few candidates out early; outright defeat in a nomination caucus or primary, defeat at the summer convention, or defeat in November does in the others. Some losers, like George Bush to Ronald Reagan for the Republican nomination in 1980, catch a caboose to victory. The 1980 GOP nomination night in Detroit was confused. Remember the dalliance with President Ford over the No. 2 spot? Reagan and Ford, formerly bitter rivals, were to ride off into the sunset together, in a kind of joint presidency. When that notion evaporated, Reagan had to accept Bush - precisely what some of Reagan's own people had hoped. From the vice presidency, Bush's starting block wa s set out ahead of everyone else's for 1988. Since Bush says he will run again, health permitting, and since Bush's physical and political health are both sound these days, would-be challengers have to think hard about taking him on. A challenge from within his own party? What for? To position for 1996? Is there another Ronald Reagan, who challenged Ford in 1976, in the wings? Today's dissident GOP base slumbers. The natural heir to George Bush is Secretary of State James Baker, not Vice President Dan Quayle. Baker has been engineer, thinker, and doer behind Bush's national success. Dan Quayle, as vice president, is the nominal heir. How will this drama of institutional advantage and loyalty work out? Will Jack Kemp and the populist wing of the party, Reagan's roost, again attack the privileged set of Quayle, Baker, Ltd.? Next, why should a Democrat take on such heavy odds? Might Bush self-destruct by November 1992? Should a Democrat position himself for '96? Reagan's loss to Ford in 1976 did not keep him from beating Carter four years later; the losing campaign taught his people much for later success. Jay Rockefeller, the Democratic governor of West Virginia, has the time and resources to wage an eight-year campaign. Mario Cuomo, the New York governor, has the intellectual and oratorical gifts, the high energy, to campaign nationally. Cuomo muses that the time might not yet be right for an ethnic-oriented campaigner - even as America undergoes renewed immigrant diversification. Rockefeller has just finished a report on children's needs, a task more akin to philanthropy than to hard politics; he is jus t testing his aggressive campaign voice with criticism of Bush: How will that voice develop? Bush has done many things well, but not every thing well. He has presided ably during the Soviet shift from an ideological, warrior state, to cooperative, beggar status. This is ironic, like Nixon in China, given the anti-communist start of the Reagan-Bush era. Likewise, Bush has put aside the Latino-phobic legacy of 1980 (started by revolution in Nicaragua, a Latino horde was imagined sweeping north through Mexico); he is promoting a North American trade zone that embraces Mexico and Canada. Is Bush vulnerable? He could be blindsided by something like the Irangate scandal of the second Reagan term. More certainly, he has not shown the high compassion a leader should show toward minorities and toward those left to scramble for work. His nomination of Clarence Thomas, a conservative black, for the Supreme Court, threw salt on relations with black leaders; many Americans are finding life tough, even after a college degree. The basic American political dynamic is between the themes of "individual freedom," which Reagan and Bush rode to victory, and "equality," stressed by Johnson and Carter. Neither theme is owned by either party. Republican Abe Lincoln and Democrat Franklin Roosevelt were the great "equality" presidents. The swing to the equality theme again is certain, if not its timing. It is worth risking a loss or two to be ready when its occasion arrives. Worse than losing would be to sleep as history passes by.