WHEN THE OPENING salvos were fired, campaign 1982 looked like a referendum on national economic policies. The Democrats fearlessly assailed Reaganomics, while the Republicans asked voters to "stay the course." In state after state, these themes have been echoed in elections for senator, congressman, governor and even state legislator.

But after these brave opening lines, the debate on national issues seems -- on both sides -- to be sputtering. The Republicans have not presented, as they did in 1980, a plausible scenario of how we will get from the here of an unsatisfactory economy to the there of a satisfactory one. The implication is that current policies will get us there -- something on which many voters, not all of them partisan Democrats, have doubts.

The Democrats do not even have a policy to suggest. As the party out of power, that is, of course, their privilege, and perhaps the donkey can prevail just by braying about the evils of things as they are. But that leaves the Democrats with little to talk about, except for proposals for marginal changes from the Reagan policies.

So we find the debate moving from national to local issues. The president himself leads the way. In Des Moines, he brags about how much grain he has agreed to sell the Russians. He announces an agreement to limit steel imports, which his press secretary says "will give us a boost in Youngstown and other hard-pressed steel-producing cities." Never mind that neither of these initiatives is consistent with what Mr. Reagan has proclaimed for years as the basic thrust of his national policies. Like the Democrats he criticized for the same tactic, he is treating the electorate as a collection of disparate special interests, and trying to buy each of them off with a bit of government largess. He can hardly complain if other candidates, Democrats or Republicans, do the same.

So the campaign, regardless of the partisan outcome, is likely to have a centrifugal effect on national politics. That is the opposite of 1980, when Mr. Reagan and his Republicans won a national victory on a reasonably coherent national platform that addressed the major national issues. Now we are likely to see more of the politics of every-man-for-himself, of particular states and districts seeking government aid and advantage, regardless of the effect on national policy. Mr. Reagan, having campaigned on at least some of these issues himself, may be in a weaker position than he was earlier this year to resist the parochial and to assert, as the one official elected by the whole nation, a national perspective.