WITH A STROKE of Gov. Harry Hughes's pen, the southern regional primary became a reality on May 27. Ten states will be voting in the second week of March 1988 -- the first week allowed under Democratic party rules -- in caucuses and primaries to choose their presidential convention delegates. The North Carolina and Louisiana legislatures will probably add those states to the list in the next several weeks, and Arkansas and Texas may do so next year. More than one-third of the delegates will be chosen in one wintry week. This will transform the presidential delegate selection process and the political landscape.

At least two interesting questions remain. One is whether the southern regional primary will alter the political landscape in the ways intended by the southern Democrats who were the moving force behind it. They feel aggrieved and without a champion in Democratic presidential candidate ranks (even though the Democrats nominated a southerner in two of the last three elections), and they want to see someone such as Sam Nunn or Charles Robb in the race. But the southern regional primary could result in a strong finish for Jesse Jackson on the Democratic side and evangelical candidate Pat Robertson on the Republican -- candidates who, respectively, repel and attract just the kind of rural, tradition-minded white voters the southern Democratic politicians need. Regional primary advocates argue that it will lead candidates to tailor their appeal to southern sensibilities. It may. But there is no mechanical way to guarantee a particular political result.

The other interesting question about the southern regional primary is whether it will remain southern and regional. Other states are switching to earlier dates as well. It has gotten to the point that one leading expert on delegate counts is arguing for a straightforward national primary in May, with a runoff in June. We have plenty of reservations about a national primary. But the trend may be heading that way.

In the meantime there is the prospect of a southern regional primary with two fields of little-known candidates. That means a campaign -- a series of tests of character and issues -- that begins in the fall of 1987, takes a recess for the holiday season and then goes full blast the first nine weeks of 1988. This is what the southern legislators have wrought.