MUCH IS CLOUDY, but a couple of things are clear about Mr. Reagan's plan to strengthen the American naval presence in the Persian Gulf. The president, when he announced the plan, had not thought out the what-ifs, the different ways events might unfold. And Congress was looking the other way.

All that changed with Iraq's attack on the USS Stark on May 17. Suddenly a situation that appeared to be a remote strategic chessboard became as well a battlefield on which real American lives were being lost. Pressure mounted on the administration to show it was alert to both kinds of considerations: the risks of involvement as well as the reasons for involvement. Congress shook off the cobwebs and began asking the questions it had previously passed by.

What has been learned in the six weeks of debate since? One unsurprising discovery is that Congress is nervous on the merits, uncertain whether the possible risks of putting into effect President Reagan's reflagging plan are greater or less than the likely costs of now backing off. At the same time, Congress hesitates to assert a policy role of its own: it is ready to raise questions but not to assume responsibility either by supporting or blocking the president's plan.

What is further evident is that President Reagan seems short on the determination needed to push his own plan through his own administration, let alone through Congress. Different estimates of the risks come from different departments. The oil equation is variously calculated. The military mission -- whether to protect Kuwait's shipping, Kuwait-bound shipping or all neutral shipping -- shifts. There is no untangling of the contradiction between promoting the broad goals of free navigation and the free flow of oil and taking specific steps that encourage Iraq to block the navigation and oil of Iran. No coherent reply is offered to whether Moscow is, in the Gulf, partner or rival.

The Gulf is a vital region. It is worth taking risks to preserve an American position there. It can only damage the United States to be seen being kicked out of a third area -- the Gulf, after Iran and Lebanon -- by the Ayatollah Khomeini. But the risks must be understood and accepted at the beginning of any course of action -- understood not just in this country, but also in the places where the United States would be obliged to carry its policy through. This is the burden that the administration has failed to discharge, even as more American warships daily steam closer to the Gulf.