A US presidential election - the next a year away - is the great simplifier of the American political equation. Other races are significant, too. In 1984, with a near-even chance the Democrats will regain control of the US Senate, the prospect of a standoff between a reelected GOP President and a Democratic Congress cannot be ignored. State and local races could show their own crucial tides.
But it is control of the White House that remains the big prize, and therefore the preoccupation of politics buffs - even if they do try to draw too much from each day's events.
Viewed another way, there is no more vital public task than for citizens to weigh the daily evidence about their leadership choice, whether they make up their minds at the last moment, as most do, or not.
Political pros in both parties use almost the same words in sizing up the 1984 race. Republicans are feeling more upbeat than ever about Reagan's chances if he runs again. ''But it's not a foregone conclusion he would win,'' says one GOP professional slated for a command post in a Reagan campaign. ''Nothing is a foregone conclusion, even whether Reagan will run,'' says a similarly slotted Democrat.
The latest GOP electoral vote estimate has Reagan leading Mondale in a hypothetical race by 10 votes, 216 to 206 with 116 in doubt. Reagan trails Glenn by 49 votes, 180 to 229 with 129 in doubt. The state by state electoral tallies reflect how a president is actually elected, with 270 electoral votes needed to win.
As expected, Reagan leads both Mondale and Glenn by 100 to 11 in the West. He trails both Mondale and Glenn by 30 to 83 in the Midwest and by 19 to 78 in the East. Reagan's margin over Mondale appears in the South, where he leads 67 to 34 . Glenn bests Reagan in the South 57 to 31, but with 86 South and border state electoral votes still rated a tossup.
Such electoral counts are of course only approximations. The current reading shows Reagan ahead of where he was in February, but remarkably close to last December's White House computer count. There's enough margin in the ''in doubt'' or ''tossup'' category for a president, with the leverage of incumbency, to hold onto the office in a tight race.
Reagan appears in even better shape when the election is viewed on thematic grounds, Democrats concede.
Reagan's theme in '84, Democrats expect, will be to say: ''I promised I would cut taxes, and I did. I said I would reduce government spending and government influence on our lives, make the US militarily strong, and I did.'' His agenda has been clear. He succeeds where he can make a simplistic argument stick, Democrats say.
Reagan will argue his policies, causing hardship for some, were designed to help everybody, not separate constituencies to which Democrats habitually appeal. This could prove a persuasive argument, Democrats say, even though they feel a closer reading of Reagan's programs would show fewer results than he will claim.
Any Democrat - meaning Mondale or Glenn - would beat Ronald Reagan in the Northeast right now, both sides argue. Elsewhere, black registration will be up. Blue-collar whites in Alabama, Mississippi, Tennessee, Kentucky will vote more Democratic in '84 than they did in '80.
Still, '84 will be a tough election for the Democrats, they admit. ''The Democratic Party will have to convince middle-class Americans that the obvious gripes of interest groups also have meaning for them - or that though not personally affected, it was unjust or unfair for others to have suffered so much ,'' one Democratic professional says.
Reagan has gained a month or two of time from the Korean jetliner incident to act presidential, Democrats reason. He was in trouble in foreign policy - Poland remains in a quagmire, the Middle East at the moment could be more explosive than at any time in the last decade, conflict builds in Central America, and the Soviets are still in Afghanistan despite the protests of the administration. The jetliner disaster has given Reagan a breather, stilled the opposition at home.
''The test of Reagan's performance on the jetliner was whether he avoided a rash action,'' a Democrat complains. ''A more objective reading of Reagan's performance in world affairs is that the world is a more dangerous place, with less American control, than when he took office. But I'm not sure that that tells against the message he communicates. The jetliner episode enables him to say 'I told you so' about the Soviets. He has combined hot rhetoric and cool action, giving America less leverage than before.''
Elections, of course, occur in the eye of the voter, not in the assessments of partisans. The Democrats hope for a substantial enough discounting of Reagan claims, plus their own ability to relieve voter doubts about Democratic solutions, to turn the election their way.
Republicans have not solidified their own expectations for '84. ''Glenn looks like a little stronger candidate,'' a GOP pro says. ''But if he continues to run such a poor race for the nomination, how can he run a good campaign against Reagan? And if Mondale runs through Glenn for the nomination, how can we assume he will be a pushover for Reagan?''
Surely there's enough in all this to merit close public attention, even though the seemingly endless American presidential campaign tests the endurance of all but the most avid politics buffs.