THE VIOLENT CLASHES reported over the weekend in South Korea suggest yet another burst of democratic protest and offficial repression. But this time there's a difference. President Chun Doo Hwan last Wednesday made a major concession to the opposition and accepted its insistent demands to permit a constitutional amendment before his term of office expires in 1988; his condition was that the opposition keep debate ''within the framework of law and order'' and halt its street campaigns. The opposition, however, refused to call off a rally that had been scheduled for Saturday in Inchon, declaring that President Chun's willingness to consider constitutional change fell short of its demand for a turn from indirect to direct presidential election. And on the way to the rally, according to independent observers, students and workers acting in defiance of moderate opposition leaders created the provocations that brought police firing tear gas to the scene.

The sequence indicates just how delicate the situation in South Korea is. That President Chun, a former general who took power in a coup in 1980, rules with a heavy hand is undeniable. It took, evidently, the example of Philippine president Ferdinand Marcos' fall and the imminent visit of Secretary of State George Shultz, who arrives there Wednesday, to move him off his dogged refusal to consider the opposition's request for constitutional change. The change is required, the opposition argues, to keep the president from in effect naming his own successor.

The opposition, however, has a certain all-or-nothing bent that does not make change come easily even when the government pronounces itself ready for it. The conduct of the students and workers on Saturday lends some substance to official charges that the opposition is exposing the country to disorder that communist North Korea might somehow exploit. Some opposition figures, such as Kim Dae Jung, appeared at a press conference last week to decry the ''radical leftist ideas,'' such as anti-Americanism, found among some students. But even Mr. Kim, in an article on the opposite page today, rejects the new offer of President Chun, declaring that there can be ''no compromise on how the Korean people should be allowed to choose their own president.''

President Chun speaks for a conservative military establishment that is obsessed by the communist security threat the country undeniably faces and prone to question the opposition's patriotism and to oppress it at the slightest provocation. But his turnabout offer to consider prompt constitutional revision, while hedged, does appear to represent the sort of readiness for dialogue that must be at the heart of any process of orderly decompression from tight military rule. The Korean opposition has a compelling cause, democratization, and many brave and worthy advocates. It also needs to show an appreciation for tactics, lest it end up not with more democracy but with less. The American role, which Secretary of State Shultz will be conducting on the ground this week, is help keep Korea moving steadily along the democratic path.