For US, two big questions answered, but one still lingers. Clarity on Soviet Union and S. Korea, but not on Gulf

The past week in world affairs has seen the clearing away of two big uncertainties. There is not going to be a blood bath in South Korea. And there is going to be a major push in the Soviet Union for radical reform of the entire economic, social, and political system.

A third important uncertainty remains: Will the Reagan administration be able to go ahead with its plans for the Persian Gulf in spite of its remarkable inability to explain rationally to Congress what it wants to do there and why.

The key moment in South Korea came on Tuesday, when riot police in Seoul and Kwangju packed their gear and went back to their various local posts and duties. The fighting and rioting was over. The Army would not be called in to suppress political opposition.

We do not know yet just how President Chun Doo Hwan was persuaded to refrain from taking the drastic measures that were being threatened, and presumably contemplated, as late as June 19.

On that day Lee Han Key, Mr. Chun's prime minister, stated that ``the students and citizens who have taken to the streets must refrain from disorderly collective action and return to their homes and workplaces.'' He added that if it becomes ``impossible to restore law and order,'' then it would be ``inevitable for the government to make an extraordinary decision.''

On June 20, the rioting continued.

On June 23, an assistant secretary of state arrived from Washington.

On June 24, Mr. Chun received Kim Young Sam, leader of the main opposition political party.

On July 1, the government released political prisoners and agreed ``in principle,'' but on a ``probationary basis,'' to constitutional reforms that would allow voters directly to elect a president.

Was the arrival of United States Assistant Secretary of State Gaston Sigur the decisive act in defusing the crisis? If so, the hand was played more delicately than in either the Philippines (dethronement of the Marcos family) or in Haiti (dethronement of the Duvalier family.)

There is no dethronement in South Korea, but there is abandonment of a plan to impose the next president without a direct election. A step is to be taken toward democracy. The ability of the dictatorship to perpetuate itself through nondemocratic means is broken.

In the Soviet Union, the important new event was the display of Mikhail Gorbachev's effective control over the Politburo, the inner executive committee of the Communist Party. Three new voting members and one nonvoting member were announced, giving Gorbachev a new Politburo. Of its 14 voting members, eight owe either their membership or their promotions to him. Four of the six candidate (nonvoting) members are also his men. He has consolidated his power.

The consolidation was displayed by the prompt, and unanimous, approval both in the Politburo, and later in the party's Central Committee, of Mr. Gorbachev's plans for radical change in the Soviet system.

The legislation is now in place that mandates a program of progressive change that, if carried out, will mean the decentralization of the economy; independence and responsibility for factory management; the fixing of prices by the market; the possibility of bankruptcy; and dismissal of employees for incompetence or nonperformance.

This program, if it is put into effect, would be the biggest change in the Soviet system since Joseph Stalin set the mold. It would mean a long step back from full Marxism. It would mean the revival of economic incentives in the Soviet economy. It would take away from thousands of party members the juicy jobs that provide them with their privileged role in Soviet society. It would be the beginning of the dismantling of the Stalinist state.

Until this week, there was doubt in Washington that Mr. Gorbachev could carry out such a program, even if he were sincere about wanting to execute it. Most of the basis for such doubt is now removed. The legislation that is needed to execute the program is in place and officially ratified and officially proclaimed. There is no longer room for doubt that Mr. Gorbachev is pushing ahead for major change in the Soviet system.

As for the Persian Gulf, administration officials in Washington this week were contending that Congress should support its plans for putting US flags on 11 Saudi tankers, on the ground that failure to do so would mean handing the Gulf over to the Soviets. It would mean no such thing. There are three or five - reports differ - Soviet ships now operating in the Gulf. They are small ships. The Soviets say they have no intention of increasing the number. There are more than five US vessels on routine patrol in the Gulf. There are also British and French naval vessels on routine patrol in the Gulf.

There is no logical reason why the display or non-display of US flags on 11 Kuwaiti tankers would make a difference in the relative position of the US versus the Soviets in the Gulf.

It is to be noted in this connection that, while the Soviets have leased three tankers to Kuwait, they have also been in active diplomatic contact with Iran. They sent Yuli Vorontsov, a deputy foreign minister, to Tehran in early June, presumably in the hope of heading off any trouble between Soviet tankers and patrols and Iranian military sea and air craft.

The Soviet position in the Gulf is diplomatically better off than the American in that the Soviets are in touch with both belligerents and are avoiding the appearance of taking sides against Iran in the war in the Gulf.

The US, by contrast, is taking only the military step of planning to protect the 11 tankers by an increased US naval presence. It has not, so far as we know, attempted to reopen diplomatic relations with Iran. Hence the US will be in a position of trying to limit Iran's ability to make war on Arab shipping in the Gulf. This amounts to siding with Iraq against Iran. Congress is not forbidding the operation, but not even the Republicans are willing openly to support it.