LAST THURSDAY, Democratic National Chairman Paul G. Kirk Jr. came out against a 1986 party mid-term conference or "mini-convention" of the sort the party had in 1974, 1978 and 1982 on the grounds that it was a potential breeding ground for political "mischief." The reaction was a collective sigh of relief from the leaders of the Democratic party.

There should be a similar reaction to the fact that Kirk also opposes any extensive changes in the party's presidential delegate selection rules, which have also proved to be breeding grounds for political mischief, some unintentional, some calculated. Maybe the Democrats are about to break some bad habits.

Since 1968, the Democrats have enacted so many rules "reforms" in an effort to open up the party, make it scrupulously fair to absolutely everyone and shorten the presidential nomination process that they call to mind the story about the error- prone outfielder who finally was replaced by a teammate. The replacement proceeded to make three consecutive errors. His disgruntled explanation was, "Al got the position so screwed up no one can play it."

What the Democrats' reforms inadvertently did was help make the process longer and more costly by encouraging an increase in the number of primaries -- they about doubled during the 1970s -- as a means of opening up participation to everyone. The reforms also split the party between regulars and reformers, antagonized many in the middle class and thereby may have contributed to the Democrats' losses in 1972, 1980 and 1984 and their deep current political malaise.

Since it obviously is more expensive to campaign in a primary state than deal with a handful of party bosses who can deliver their delegates (as John F. Kennedy did with Chicago Mayor Richard Daley in Illinois and Michael V. DiSalle in Ohio in 1960), the candidates have to get out early to raise money and compete for voter attention through increasingly frequent -- and early and spurious -- state and local party straw polls. Even in the non-presidential primary states, the candidates' campaigning for the caucuses more resembles primary politics than the old smoke-filled rooms.

Many of these unanticipated side effects have been codified under what has come to be known as the "Law of Unintended Consequences." More to the point right now are the changes in the process that had intended consequences -- the "front-loading" of the primaries to benefit the front- runners for the Democratic presidential nomination in 1980 and 1984 who could raise big money early.

In 1980, Jimmy Carter's supporters rigged the schedule of that year's primaries so that there were a number of early new Southern primaries -- Alabama and Georgia among others -- to help him against the challenge of Sen. Edward M. Kennedy (D-Mass.).

Kennedy's supporters went along with some rules changes designed to keep small-fry candidates out, particularly the one raising to 20 percent the the percentage of the vote a candidate needs in a primary or caucus to qualify for his proportionate share of delegates.

In 1984, these rules were supposed to work to Walter F. Mondale's benefit, and to an extent they did. His razor-thin victories in Alabama and Georgia on the March 13 "Super Tuesday" gave him the spark of political life to make his dramatic comeback.

In the name of shortening the nominating process, the Democrats changed the schedule so that the New Hampshire primary was only eight days after the Iowa caucuses rather than five weeks, as in the past. Instead, this helped lengthen the primary process by making it even more imperative for the candidates to raise early money and support.

It should have enabled Mondale to exploit his Iowa victory in New Hampshire by almost eliminating his opponents' recovery time.

Pat Caddell, who advised Sen. Gary Hart (D-Colo.) last year, contends that if that back-to-back schedule had been in effect in 1980, Ronald Reagan might not have been the Republican nominee because he wouldn't have had time to overcome George Bush's surprise victory in Iowa.

The 1984 schedule couldn't offset Mondale's weakness as a candidate, however. It just pointed it up because Hart, who got only 15 percent of the Iowa caucus vote, beat Mondale handily in New Hampshire and in Massachusetts and Vermont and Maine as well.

Caddell, who has encouraged Sen. Joseph Biden (D-Del.) to pursue the Democratic nomination, has a plan to offset the current front-loading of the schedule. It would give weaker or late-starting candidates -- such as Hart in 1984 and perhaps Biden in 1988 -- a better chance by giving the winners of the middle primaries more than their proportional share of delegates and making the late primaries winner-take-all.

Caddell is right in his concern that the nominating process not be arbitrarily foreshortened for the advantage of front-runners as previous rules have attempted and that it be allowed to run its full course. No one, however, can even guess at this point at the unintentional consequences Caddell's radical proposal would have.

Kirk favors a couple of relatively minor rules changes, but he'll have his work cut out to hold the line against those who mistakenly think the presidential election season still is too long and costly and want to try, again, to remedy it by changing the rules.

There is a new group in the field, the Commission on National Elections (CNE), sponsored by the Center for Strategic and International Studies, which in its statement of purpose suggests that the presidential elections "take too long, cost too much and succeed in attracting too few Americans to the polls" because they become bored with the process.

A lot of Americans, including many members of the large, bipartisan CNE, agree with this misguided notion. Along with death and taxes, it is sure that both the CNE and the Democrats' Fairness Commission, which is officially commissioned to review the party rules and recommend changes, will seriously consider measures to try to shorten the process.

At the top of the list is regional or time-zone primaries, which are envisioned as boiling the presidential nominating process down to a handful of "Super Tuesdays." They ignore the difficulty of getting the state legislatures to change their election laws to make this possible. Also, the plan would increase the pressure on candidates to get out and raise money early.

Before the Democrats (Republicans are excused because all the rules changes are dreamed up by Democratic reformers and enacted by Democratic-controlled state legislatures) do anything they all should take a deep breath and lie down on the couch until the feeling passes.

They should start by considering the proposition that three months isn't an inordinately long nominating season for a nation of 235 million people. As to the cost, preliminary estimates are that all 1984 elections, from presidential on down, probably cost around $1.5 billion, about $6 for each man, woman or child, just a fraction of what we spend on cosmetics, pet food and illegal drugs.