INTERNATIONAL patience with North Korea's endless brinkmanship is wearing thin. American and South Korean willingness to go the extra mile have so far produced little result. The secretive North Korean communists have suspended their threat to withdraw from the International Atomic Energy Agency and offered to open some minor nuclear sites for inspection. But the crucial sites the agency believes will show if Pyongyang is on the point of making a bomb - or already has several - are still off limits. In frustration, Washington is considering asking the United Nations for an oil embargo. But officials can only guess if sanctions would enjoy international support. Russia has hinted it will oppose sanctions against its former ally. China, also an ex-friend of Pyongyang, has done more than hint. Both have a Security Council veto. Yet big Chinese cities are as much within range of North Korean weapons as Tokyo or Seoul. So White House Chief of Staff Mack McLarty's belief that China might join an embargo may be closer to the mark than it seems. But there is even less guarantee an embargo would be effective. Even if China chose to support trade measures, its long border with North Korea leaves scope for sanctions-busting and corruption. North Korea is more isolated than other countries which have been subjected to sanctions in the past, and its economy is more vulnerable. But its few remaining friends - notably Iraq - are major oil producers, and desperate for markets. Embargoes are notoriously prone to stiffen resistance and raise national resolve. Given its ideological devotion to self-sufficiency, and its resulting economic collapse, North Korea probably has little further scope for defiant introversion. But Russia's argument against sanctions - fear that an embargo could lead to war - is also a concern in the United States. Some observers fear the Pyongyang regime is crazy enough to try it. President Bill Clinton has warned America would annihilate North Korea if it used nuclear weapons, but the confused signals the administration has been sending since are a sign of its indecision and frustration. Sanctions might still be the best demonstration of international resolve. But an attempt to impose them without widespread support would be another US foreign policy disaster. So, too, would ineffective sanctions like those now imposed on Serbia. After Yugoslavia and Somalia, the US administration will think twice before taking populist but premature action. These days the ''feelgood'' factor wears off with uncomfortable speed.