Democratic political strategists continue to pursue their glittering vision of the trade issue. The question for 1986 -- and later -- is whether it will prove to be, politically, more than a mirage.

For this is not the first time that Democratic politicians have glimpsed on the horizon the vision of an issue that makes them appear at one and the same time nationalistic and assertive, compassionate and responsive, far-seeing and populistic. More than a decade ago the Burke-Hartke bill was going to win elections in the early 1970s for the Democrats; now it seems unlikely to make the history books. More recently, the Democrats went on a trade offensive last summer. They did take one important scalp: an errant remark by an inexperienced Republican candidate ("I don't see what trade has to do with east Texas") helped the Democrats win a Texas special congressional election -- a victory that discouraged Republicans from running in southern Democratic districts elsewhere. But that was a close race in which any mistake on any issue by either candidate might have tipped the balance.

Now Democratic Congressional Campaign Committee chairman Tony Coelho (D-Calif.) sees trade as a key Democratic issue in a number of states. Democrats hope for gains in North Carolina, which has a lot of marginal districts, South Carolina, Pennsylvania and Maine. Republican congressmen are either on the defensive or joining in support of the Democrats' latest trade bill. In these states and others, trade is particularly welcome to Democrats as an issue that makes them look tough and truculent, rather than soft and generous.

But is there a chance for anything more than scattered gains? Trade is not one issue but dozens: textiles in the Carolinas, steel in Pennsylvania, shoes in New England. A local Democrat in any one election can claim to have a magic answer to save an old industry. But a national party, seeking to run a national government, will be asked for a policy that fosters economic growth generally rather than one that seeks somehow to preserve the past. Once again the Democrats are marching across the desert, trying to reach a trade issue that glitters before them. It may again turn out to be a mirage.