TU.S. policy in Central America faces a critical challenge this week.

It is a challenge that far surpasses the question of whether Congress will allow $14 million to be spent on behalf of the Nicaraguan resistance. It is a sign of whether the United States is prepared to be involved effectively in the region during the coming years.

Even if the $14 million should gain congressional approval, it would not constitute a policy toward the region. It would be the first step on a longer journey toward achieving a measure of peace, prosperity and justice for the long- suffering people of the region.

This is the dilemma that Congressional deadlines and certifications create for American foreign policy: they exaggerate out of all importance relatively small decisions. Having structured an all-or-nothing outcome for our support for the Nicaraguan resistance, many in Congress now wonder why the president attaches so much importance to this vote. And they seek for ways to skirt the crisis they have created.

The fact is the United States will have to undertake a long and difficult series of tasks if we are to succeed in Central America. But having come to the present pass, it is important that the president succeed. Congress' actions during the next several weeks will be taken as a statement of long-term American intentions for the region. If the United States turns away from the Nicaraguan resistance, many parties will conclude that we do not have either the heart or the stomach to remain involved in the region in an effective way. And that would be a tragedy for the people of the region.

It is not simply the Nicaraguan resistance that depends upon the outcome of this vote; our friends and our foes in many nations will draw their own conclusions as well.

Will those who have remained in Nicaragua to express their brave opposition to growing Sandinista political control derive encouragement from our turning away? Will those whose investment and entrepreneurial talents are necessary for the development of every Central American nation conclude that it is wise to risk their lives, their families and their fortunes in Central America? Will friendly neighboring nations who have looked to the United States for support of their democracies -- and found it up until now -- conclude that it is safe to resist Sandinista threats?

There is already evidence enough that many have chosen to find their futures elsewhere. Several hundred thousand refugees have left Nicaragua, and we should expect many more if we offer no incentive for them to stay. The time is long past when innocents, or those who profess innocence, can take comfort in the vague hope that totalitarian regimes will produce non-totalitarian results. The specific type of mass exodus from Marxist-Leninist practices is depressingly familiar.

And what of the Sandinista government? What lesson will it draw from American refusal to support the resistance? To think that liberalization will be the answer is simply incredible. The Sandinista government has demonstrated for six years that it is prepared to expand and to consolidate its control just as far as it can safely do so.

Without the resistance, the Sandinista government can expand that control with impunity. That is why both Nicaragua's neighbors and those who still speak for freedom within Nicaragua are concerned that they will be the next targets of an unopposed Sandinista regime.

The Sandinistas have no cause for complaint against the United States. The United States helped to remove their predecessor, Anastasio Somoza. The United States greeted the Sandinista government in 1979 with generosity and with a sincere desire to cooperate in fulfilling the stated goals of the revolution. The United States joined other Western nations in providing to Nicaragua considerable economic assistance.

What was the result? The Nicaraguan government turned toward the Soviet Union and Cuba, as if turning its own nation into an economic shambles and an armed camp were somehow a sensible response to these efforts.

We need a broad-guage policy toward Central America. At this juncture, we are unlikely to get the policy we seek if we turn our backs on the one force that has demonstrated it can command the attention and the concern of the Sandinistas. Support for the resistance is a critical element of a policy that has any realistic hope of bringing about the ends that all Americans expressly desire.

Support for the Nicaraguan resistance is a difficult proposition for many Americans. For many years, it has been charged -- with some justice -- that the United States supports the status quo and an overly fearful view of change around the world. That the United States should now, calling for free and democratic institutions, support revolutionary change is a courageous course in Nicaragua. But perhaps in light of the opposition movements demanding freedom in Kampuchea, Afghanistan, Ethiopia, Angola and elsewhere, it should not be so difficult to comprehend that our interests can be served by fidelity to our own dynamic, revolutionary heritage.