SPEAKING OF Republicans: the candidates for the GOP presidential nomination in 1988 have all made themselves, in different ways, hostages to the course of the economy over the next three years. Each has identified himself -- or put himself in a position where he is bound to be identified -- with an economic program that not only prescribes particular policies for the future but predicts what the future is going to look like. Plausible cases can be made for each set of prescriptions and predictions today. But these cases are not likely to seem equally plausible 2 1/2 years from now.

Senate Majority Leader Robert Dole, who has been rising in presidential polls this year, has made no secret of where he stands. He wants to cut the deficit and thinks the nation faces dire economic consequences if it continues at the $200 billion level. Underlying this stand is an assumption that, absent the deficit problem, things will go tolerably though not necessarily spectacularly well. You may need to adjust farm programs and you may want to get more generous with food stamps -- both causes championed by Mr. Dole -- but you don't need to make major changes to get America moving at a decent pace again. These views will be tested by events. If taxes aren't raised and spending not cut much, and deficits continue with dire consequences, Mr. Dole's view will be vindicated. It will also help if he manages to lead Congress in the direction he attempted this year, and things get better. But if deficits continue and the negative payoff does not come in time for him politically, Mr. Dole's stock will fall.

Similarly, events will test the quite different economic theories of Jack Kemp. Mr. Kemp is brimming with confidence that the American economy will grow exuberantly, if only it is freed from the shackles of high taxation and tight money. Mr. Kemp wants something like the present administration's fiscal policies coupled with something like the pre-Paul Volcker monetary policies. Some of his policies -- the Kemp-Roth tax cut, most of which Mr. Reagan got through Congress in 1981 -- have already been tested, and have so far conspicuously failed to produce the sharp rises in investment and high levels of sustained economic growth Mr. Kemp predicted. He doesn't have much more time for them to work out.

As for George Bush, he is in the odd position of being held accountable for the success of Mr. Reagan's policies even though almost everyone supposes that he would have done things at least somewhat differently himself. He did, after all, coin the phrase "voodoo economics" in 1980. Yet politically, Mr. Bush will probably be seen, and seen accurately, as the closest thing to a Reagan replica in the 1988 race. If growth is high, inflation low and unemployment not rising, Mr. Bush's candidacy will be helped, as Richard Nixon's candidacy was by similar conditions through much of 1960. If the economy stumbles, he will be hurt, as Mr. Nixon was in the fall of that year.

Of course, other things will affect the outcome: the strengths and gaffes of the candidates, their stands on other issues, the nature of the particular Republican electorates, the skills of their campaign operations. But to an unusual extent these three Republicans, who are currently leading in polls for 1988, have made themselves hostage to the economy and the turn it takes in the next couple years.