All through the period of gathering American anxiety about access to Persian Gulf oil, the premise has been that what we most lack is muscle, usable military power on the scene. That is where the administration's catch-up work -- arms, deployments, "bases," defense increases, rapid deployment force -- has gone. But the latest stage in the Iran-Iraq crisis, with the United States coming directly to the defense of Gulf states threatened by a spillover of the war, suggests that what we most lack is political ideas.

The difficulty starts, I think, with a general failure to distinguish between old interests and old wars, especially Vietnam, and new ones.

For a generation after World War II, Americans had the margin of power to take for granted the considerations -- after homeland safety, resources and markets -- that dominate the foreign policies of most lesser states. We inscribed as "vital," worth enough to go to war for, the political allegiance of nations of no relevance to our economic fortunes. We could afford anti-communism or -- to use its other name -- interventionism. At that point intervention became a dirty word.

Now we no longer have that same margin of power, though Ronald Reagan conspicuously pines for it. More than that, we find ourselves dependent on foreign resources -- oil is merely Exhibit A -- in fragile places. More than that, we find ourselves with a military establishment and a state of mind that make it hard either to conduct or to justify intervention to secure precisely those resources we now deem "vital."

The military establishment we can do something about, by degrees, though there is still no sensible official statement available on how we can usefully bring military force to bear in the varied contingencies likely around the Persian Gulf. Whether, strictly from an operational veiwpoint, we are preparing the right interventionist tools must trouble strategist and citizen alike.

What is more troubling are the concepts taking shape, or not taking shape, to guide use of those tools.

With post-Afghanistan adrenalin flowing, President Carter last January applied the critical "vital" designation to Gulf oil -- who would quibble? -- and vowed that if necessary the United States would use force against threats to it from an "outside force." He has now gone a huge step further by actually committing American forces to a war zone and assigning them a combat mission against a threat from inside the region.

This is not, strictly speaking, anti-communism, though there is a taste of it. It is securing resources. Yet it unquestionably is intervention, whether you believe that to be a wise, necessary and overdue display of American power or whether you go on to wonder, as I do, just where it's taking us.

For there is an interventionist logic to protecting resources at least as compelling as the interventionist logic to fighting communism. If a resource is vital, does it really matter whether the peril to it comes from an outside power, from a rogue of the region or from within the country? It is a slippery slope and the proof is that Jimmy Carter, that devoted old anti-interventionist, has slid halfway down it in the last week without any sign that he apprehends the importance of his slide. He has, moreover, set up the final slide, which is to intervene in a strictly internal situation -- when a Qaddafi ousts the Saudi royal family, or whatever.

Over at the State Department, they are saying that nothing has changed -- that the latest American pledges to aid in Gulf defense were consistent with American policy even before Carter's January pronouncement. This is nonsense. The crucial distinction is between a general tendency to appreciate the importance of Gulf oil and a specific commitment to use force to keep it flowing. They are also saying that the American purpose is to defend vital interests but not to dominate the affairs of any nation in the region. That's double talk, too. If the oil is truly vital, we will have to be ready, at least theoretically, to deal with any nation that stands in its way.

This is what has happened, I believe: Events around the Persian Gulf have scared us, making us leap first of all to a military response. The dynamics of the campaign have made machismo in the Gulf the test of presidential leadership. Can you imagine, for instance, Jimmy Carter going on TV to ask people to meet the crisis by driving one day less a week? Suddenly, without thinking and talking and arguing it out, we are heading back into the intervention business with a vengeance -- in the region where the stakes could not be higher and the chances of a misstep greater.