A POLITICAL LEADER can face no more urgent, heart-rending and seemingly irresistible appeal than that made to President Reagan by four Americans taken hostage in Lebanon. Abandon "quiet diplomacy" and negotiate for our release, wrote the four, who have been innocent captives for five to 10 months in circumstances that may already have taken the lives of one if not two of their comrades. To which the White House replied that the American policy of not negotiating with terrorists "will not change."

The president is right, though it is important to be clear about what that means. The assertion that the United States will not negotiate with hostage- takers is no simple abstract display of pride and resolve. Hundreds of thousands of Americans are abroad at any given moment, many in sensitive places. All -- some more, some less -- are at greater risk if the government's conduct spreads the expectation that the United States will pay easily to reclaim those who are taken.

Scores of other governments, moreover, rely quietly on American constancy. For instance, Kuwait currently holds 17 convicted terrorists prisoner; it is evidently against their release that the Americans were seized. If President Reagan accepts the four's insistence that saving the lives of innocents "should be the primary goal," he risks immense damage to the integrity and security of a friendly state. He also sends to other would-be terrorists and other would-be friends of the United States a message of potentially devastating consequences.

To see how such a message plays out, you need only look at the weekend tragedy in Colombia. Guerrillas, evidently acting at least in part on the expectations created by the government's prior flexibility, seized the Palace of Justice. This time, however, the government decided it could not yield easily. In the ensuing shootout, dozens of hostages were killed, including 11 supreme court justices, and the whole interior balance of the nation was upset.

American citizens, especially private civilians caught up by chance in international terrorism, have an immense claim on the compassion of their countrymen and on the protection of their government. But they cannot have an absolute claim. Talks or dealings of some sort, whether they are called "negotiations" or something else, may eventually have a role in their liberation. But the president must be left with adequate tactical discretion. He alone can have the fullest available knowledge of the terrain. He alone has the responsibility to guard the national interest as well as to aid citizens in distress.