WHAT IF somebody gave a party reform commission and nobody came? This is, almost, the predicament the Democrats seem about to find themselves in. In 1984, candidates Jesse Jackson and Gary Hart extracted from the Mondale campaign support for a call for yet another party reform commission. But all the signs now are that not very many professional Democrats -- much less anyone else -- care much about it.

Part of the reason is that almost no one likes the agenda Mr. Jackson had in mind. He wanted to make it easier for candidates who had the support of only a minority of delegates, even candidates who had no hopes ever of winning enough Democratic votes to get a nomination, to be able to put sand in the gears of a front-runner's steamroller. But almost no onday believes that Walter Mondale's prospects in 1984 would have been better if he had been forced conspicuously to bow to more of Jesse Jackson's demands. Quite the contrary. Four-fifths of the members of the new reform commission will be selected from the ranks of the Democratic National Committee. It has few if any members interested in the kind of reforms (such as quotas for, among others, "persons of all sexual preferences") that Mr. Jackson seeks.

The "fairness commission," as the reform group is called, may end up focusing on other issues altogether. One is the scheduling of the Iowa caucus and New Hampshire primary. Current Democratic rules prohibit other states from holding their contests as early as these favored two. But that's not ordained in the Ten Commandments or the U.S. Constitution. The argument for the early contests is that they enable little-known, not-so-well-financed candidates the chance to campaign before relatively small electorates. The argument against them is that a minuscule number of voters can catapult a candidate who has undergone little scrutiny most of the way to the nomination and maybe to the presidency. This negative argument gains strength when you realize that many votes in Iowa and New Hampshire are given not in confidence that the candidate is up to the presidency, but because he's vaguely interesting and seems to deserve a chance to compete further.

The party's leaders hope this reform commission will complete its work by next January, well in advance of earlier commission timetables and probably before any prospective 1988 candidates can figure out how to jimmy the rules in their own favor. Let's hope they do. You don't have to agree with those who believe that the Democrats' rules, and their fights over rules, are a major reason they have lost four of the last five presidential elections to agree that endless disputes over the rules divert the Democrats from more useful discussions and thoughts. If they must get on with it, let them get it over with.