The enormously powerful American task force navigating the narrow passages of the Hormuz Strait provides a sad spectacle of the decline of U.S. power. The presence of so much concentrated military hardware is an unwitting monument to the lack of international credibility in American resolve. If American power were truly feared, not a single American warship would have been necessary. An American flag would have sufficed.

This is another way of saying that the U.S. capacity for effective deterrence has badly eroded. Increasingly, the prevailing assumption is that the United States would not dare to use its power -- whether at the conventional or strategic level. As that credibility declines, the display of American power to convince anyone of U.S. seriousness will have to grow in inverse proportions. In effect, the costs of conveying U.S. concern are inflating -- and the risk that a potential U.S. opponent might badly miscalculate is correspondingly increasing.

This condition has both global and regional implications. It could affect the stability of the U.S.-Soviet strategic relationship, and today it particularly handicaps the legitimate U.S. effort to preserve third-party freedom of navigation in the Persian Gulf in the context of the Iraq-Iran war. That effort, on the level of both military tactics and the domestic debate, illustrates why American military might increasingly lacks deterrent effect. Indeed, things have reached the point that the very effort to deploy so much power into the Persian Gulf communicates to the Iranians the impression of American unwillingness to use it.

Deterrent power is designed to convey a strategic message. Thus, it is appropriate to ask: What did the Iranians see and hear when the United States decided to reflag Kuwaiti tankers? What they saw and heard, after all, was the point of departure for their conclusions regarding our policy and our resolve.

From the vantage point of Tehran, the United States was seen to deploy considerable naval power to escort ships in a highly confined geographical area, where such power is militarily very vulnerable and has relatively little utility. Instead of intimidating the Iranians, this conveyed an American reluctance to become engaged. It signaled an American hope that the sheer concentration of military firepower would be sufficient to deter hostile action. At the same time, the domestic U.S. debate was conveying discord, indecision and even fear. The official U.S. policy was hotly contested in congressional speeches and in editorials. Congress experimented with various attempts at mandating foreign policy through legislative action -- but to no avail, except to signal division and indecision. Speeches conveyed anxiety, concern over "risks" and especially preoccupation over the possibility of new U.S. casualties.

Particularly damaging to U.S. credibility were the almost endless congressional speculations about how Iran might strike. Their bottom line was to reinforce the image of a cowardly giant, pretentiously flexing its muscles but only too ready to run for cover at the slightest indication of trouble. This was exacerbated by the growing inclination of Congress to micro-manage U.S. foreign and military policy. The mere attempt to do so by 535 would-be secretaries of state and defense contributed to a cacophony of voices that together signaled panic rather than resolve.

Iranian decision-makers (and their religious fanaticism does not preclude clever calculation) were justified in drawing two conclusions: first, American military dispositions conveyed not only a reluctance to become involved in a fight but also a hope to intimidate the Iranians by sheer presence; second, American debate, especially the congressional voices, conveyed the inclination to cut and run as soon as any American blood was shed. In these circumstances, the propitious course of action for the Iranians was to inflict some wound on the Americans and to wait for the internal spasms of self-pity, fear and breastbeating to cause an American pullout.

A great power that is respected -- in other words, a great power whose resolve to protect its interests is unquestioned -- would have acted somewhat differently. Without much fanfare, it would have concentrated adequate military power to inflict serious damage on the potential opponent and would have quietly conveyed to that opponent its intentions. In this particular case, Washington should have informed Tehran, perhaps through a responsible third party: 1) U.S.-flag ships will continue to use the Gulf; 2) the United States will respond with military means against Iranian assets if any U.S.-flag ship is harmed; 3) the United States will react similarly if any U.S. facilities are subject to Iranian-sponsored terrorist action; and 4) the United States has the capacity to destroy not only important Iranian military assets but also vital economic facilities and to impose a total naval blockade of all Iranian maritime trade. In brief, the United States can render Iran helpless in its war with Iraq. Following such a message, the United States pointedly could have sent in an unescorted freighter or tanker, even informing Tehran of its schedule.

But to enjoy the immunity that accrues to the status of a great power one must first be willing to act like a great power. It is especially important to do so when truly major geostrategic interests are involved. The Persian Gulf region is vital to the West. The West as a whole will suffer, and the U.S. global position will be endangered, if any one of the following three scenarios should occur: 1) moderate Arab regimes in the region are destabilized by fundamentalist and Iran-backed internal upheavals; 2) Iran defeats Iraq and becomes the dominant regional power; and 3) the Soviet Union becomes the principal regional arbiter, as frightened Arab regimes, appalled by U.S. timidity, in desperation turn to Moscow for protection.

The Iranian threat to Saudi Arabia in the wake of the bloodshed in Mecca could bring matters to a head. As our decision-makers ponder how to react to a possible attack by Iran, they might well bear in mind an irreversible lesson of history: by failing to act like a great power, one invites being treated as if one were not a great power.

The writer was national security adviser to President Carter.