With fin-de-Reagan fatigue upon us and, according to this month's conventional wisdom, the decline of the American empire to follow, American successes are not a hot topic. They should be. Like it or not, the United States is facing a variety of foreign policy successes around the world. The challenge is not to blow them. Since Vietnam, the United States has had much practice in managing failure. It has had so little practice managing success that it may be losing the knack.

One success has already largely been frittered away. The deployment, over strong Soviet and peace-movement pressure, of INF Euromissiles was the most important (and most underrated) American foreign policy achievement of the decade. The Soviets tried to demonstrate that, through threat and pressure, they could achieve nuclear domination of Europe and, in effect, exert a veto over NATO military deployments. American and allied steadiness demonstrated that they could do neither.

It was an achievement of the first order. Unfortunately, it is largely undone by the INF Treaty now before the Senate. Both American and Soviet INF missiles will now be removed from Europe. But the United States, separated from Europe by an ocean, needed to leave at least some Euromissiles in place to give credibility to the increasingly incredible American nuclear guarantee -- the foundation upon which NATO rests. There was, in fact, an earlier American proposal to that effect. It was swept away by enthusiasm for the zero option.

The zero option is not the end of the world (though it may in time be the end of NATO). In any case, it is too late now to do anything about it. But it does show how a foreign policy achievement can be undone by an absence of strategy (we do not want a denuclearized Europe) and of tactical nimbleness (the zero option was offered when American deployment was a possibility; it should have been withdrawn after deployment became a fact).

Another little-noticed success -- successes are harder to cover than disasters -- is the reflagging of Kuwaiti ships in the Persian Gulf. It set limits on Iranian action, greatly enhanced American influence with the oil-rich Arab states, calmed Arab security fears in the face of the Iranian threat and secured a Kuwaiti lifeline to the Arabian Sea. As a side benefit, it yielded a lesson on multilateralism, that favorite cover for isolationists. After America entered the Gulf, the allies followed. It was a convincing demonstration that the way a superpower gets multilateral allied support is not to plead for it but to lead the way.

In the Gulf our achievement could be blundered away, too, though here not by underplaying our hand but by overplaying it. There is talk of (and pressure from Navy commanders in the area for) enlarging the American mission to include the defense of any vessel, not just those flying the American flag. Such a declaration of naval warfare against Iran would invite continual engagement, would strain American resources and would threaten Congress' rare tolerance (a product of congressional paralysis rather than principle, but no matter) for this projection of American power. Expansion of the American role is the fastest way to wreck the policy.

The other generally unremarked success of recent American foreign policy is the Reagan Doctrine, under which the United States is supporting four anticommunist guerrilla insurgencies. In every one, the guerrillas are on the move. In Afghanistan, they have already achieved strategic victory. The remaining question is when and how, not whether, the Soviet retreat will occur. In Cambodia, Vietnam has begun negotiations with Prince Sihanouk to find a way out. In Angola, the annual Cuban- and Soviet-led offensive has been defeated and the UNITA guerrillas are reported to have captured the important government-Cuban garrison at Cuito Cuanavale. And in Nicaragua, the 15,000-man contra army -- which Cardinal Obando Y Bravo calls "the resistance," a term that American contra opponents like to snicker at -- has shown unexpected military ability and built significant support among the peasantry and the internal opposition. The Sandinistas have been forced into direct negotiations with them.

It will take tactical dexterity not to spoil these successes. More important, it will take some steadiness about goals. The object of guerrilla war is not to "get to yes," but to get to power. In Afghanistan, that means resisting pressure from the Soviets (and from the understandably weary Pakistanis) for some Communist role in a future government. The challenge for the United States is not to blunder away at the table what the guerrillas are winning in the field: an Afghanistan entirely out of the Soviet orbit.

But it is in Nicaragua that the American propensity to undo is on most extravagant display. The Sandinistas are in trouble: the economy is in collapse, inflation since November is at 13,000 percent, shortages are so severe that they threaten the regime's survival. As one Nicaraguan puts it, you can control people through ration cards -- if you have food to ration. The Sandinistas don't. They are so worried about contra political and military gains that two weeks ago, just as Daniel Ortega was trying to impress Congress with promises of democracy, they arrested a dozen internal opposition leaders just for meeting with the contras.

In the face of all of this enormous pressure on the Sandinistas, Congress votes next week on whether to save them by cutting off the contras. As of today, odds are that it will. If the odds don't change, the United States will have managed the most extraordinary, self-inflicted, strategic surrender in memory. Our decline will be well earned.