SOMESVILLE, MAINE -- Socked in for a day by a patch of Maine's finest fog, I found myself, appropriately, reading line by line the transcript of President Reagan's third and supposedly final effort to explain away the Iran-contra affair. I don't recommend it. One line is all you really need: ''The fact of the matter,'' the president said, ''is that there is nothing I can say that will make the situation right.''

If he had stopped right there, we would all be ahead. Instead, declaring his mission impossible, he sets out to accomplish it, seemingly unaware that almost every explanation is raising more doubts about whether the whole sorry business has been for him, as he claims, a learning experience.

He had heard it asked why he wasn't ''outraged,'' and he wants us to know that ''at times'' he's been ''mad as a hornet.'' He says anyone would be -- "just look at the damage that's been done'' -- and he's right about that. But the least he could have done is to tell us specifically what -- or who -- has gotten him so ticked off. That might have told us a little something about whether his approach to this business of being president in the year and a half remaining to him will be much different from the approach that got him into what he is now prepared to call the ''Iran-contra mess.''

True, he did sound a little sore at John Poindexter, the former national security adviser who thought the buck stopped at his desk when it came to deciding whether or not the president would approve of the contra diversion scam. But Reagan was understanding of Poindexter and of Oliver North, as well: ''{They} believed they were doing what I would've wanted done.'' And what, pray, would the president have wanted done?

Astonishingly, after letting us wonder about that for nine months, the president didn't take advantage of his prime-time opportunity to say what he thought of Ollie North's ''neat idea'' of gouging money for the contras out of profits from U.S. arms sales to the Iranians. On the contrary, he left the impression that Poindexter and North could easily have come to believe that the president would have welcomed help of any kind for the Nicaraguan ''freedom fighters'' -- that this is the sort of my-wish-is-your-command working environment that Ronald Reagan creates.

Even the things the president had to say about how he had improved the policy-making process conveyed this same sense of helplessness. ''We can build in every precaution known to the world,'' he said. ''We can design the best system ever devised by man, but in the end people are going to have to run it."

"And we will never be free of human hopes, weaknesses and enthusiasm,'' he said, almost unconsciously ticking off the root causes of his own admittedly ''stubborn . . . pursuit of a policy that went astray.''

If the president couldn't bring himself to be all that angry at Poindexter, surely he couldn't be hornet-mad at Secretary of State Shultz or Secretary of Defense Weinberger. In fact, he credited them, in a somewhat disingenuous way, with having correctly ''predicted'' that his Iranian initiative would be quickly seen by the American people as nothing more than a swap of arms for hostages.

That was by no means the main argument made by Shultz and Weinberger; their objections had at least as much to do with the folly of selling arms to any country exporting terrorism, in violation of the very policy the United States was preaching to its allies. For rejecting their counsel, the president could only have been as angry as a hornet at himself.

But he didn't say that. So who or what were the targets of his wrath? The media, no doubt; he's made that clear enough. Congress and its investigators, almost certainly, though he was at pains to patch things up with promises of a new try at bipartisanship. But the prime candidate has to be the Ayatollah Khomeini and his associates who set up the ''Great Satan'' for its great fall.

This lends a certain unsettling significance to what Reagan said right after he spoke of his flashes of hornets' rage. ''I have always found,'' he said, ''that the best therapy for outrage and anger is action.'' The implication was that he was referring to things like fine-tuning the policy-making process, his fight for the Supreme Court nomination of Judge Bork, or perhaps his cross-country campaign for a constitutional amendment to control the budget deficit.

But surely it is not unreasonable to suspect that he had something more in mind. Some consideration has to be given to the one recent action the president didn't even mention in his address -- the one that relates directly to U.S. policy toward Iran. Surely we are entitled to be a little bit uneasy about the potential therapeutic value -- to a president afflicted by unfocused anger -- of a largely unprovoked, open-ended naval confrontation with Khomeini in the Persian Gulf.