ONE OF THE games the politicians play before every election is called setting benchmarks. As a result, it often doesn't matter so much whether you win or lose; it matters whether you beat the point spread. Thus in 1972 Edmund Muskie's New Hampshire coordinator, Maria Carrier, said publicly that it would be a defeat for the Maine senator if he didn't get 50 percent in next- door New Hampshire's primary. He didn't. His 46 percent of the vote in a multi-candidate field was widely counted as a loss, and led to his withdrawal from the presidential race.

For 1986 both parties are playing the benchmark game. For Democrats it is a straightforward business. The greatest suspense about the 1986 elections is whether they will regain control of the Senate, and they have a serious chance at winning the four seats they need for that. In the House the Democrats already have working control and are likely to gain rather than lose seats. They'll lose governorships but, they argue, not to worry: a lot of them will be in small Republican states where popular incumbents are retiring, and Democrats can't hold onto them forever.

It's a good analysis, as far as it goes, but it is possibly misleading as a barometer of national opinion. Democratic control of the Senate would affect legislative outcomes (though precisely how it's difficult to say, since Senate Democrats have not presented a united front very often). But even a Democratic recapture of the Senate and Democratic gains in the House, some Republicans are arguing, would not constitute a significant ebbing of the Republican tide that has been rising most of the last 10 years.

This argument, made vividly by the president's pollster, Richard Wirthlin, is self-serving but not without merit. Almost as many voters identify themselves as Republicans now as Democrats; pollsters argue over how wide the gap is, but all admit it's narrower than it used to be. Republicans have an edge among young voters.

Next Nov. 4 the Republicans could lose House seats and still get 46 percent of votes cast for the House; they could lose control of the Senate and still get 50 percent of votes in Senate races (because 22 of the 34 seats up are held by Republicans already). Because Republicans have consistently done better in Senate than House races and better in presidential than in congressional contests, these percentages would not be inconsistent with another Republican presidential victory in 1988, even while they would produce Democratic legislative majorities.

For 1986 both parties have set reasonable benchmarks, looking toward different goals. Now the question is whether either or both will achieve them.