Say what you will about the debates, they have provided the American voter with a wealth of thoughts and impressions to take to the voting booth. Above all, the two sessions provided a matchless opportunity to see our sequestered, stage-managed president close up and under pressure.

The second debate was a guided tour through the mind of Ronald Reagan, and it offered curious, even bizarre sights: Reagan ruminating about the end of the world; Reagan painting two tyrants: the shah of Iran as an urban and agrarian reformer, and Ferdinand Marcos as the only hope for democracy in the Philippines.

He displayed his considerable gifts as a politician: his ability to laugh at serious issues like his age and to cut huge subjects down to size.

And there were disquieting shadows in the self-portrait. He is not just a sloppy manager; his indifference to the details of a scandal like the CIA manual prepared for "our" side in Nicaragua bespeaks a man so confident of victory that he does not need to explain or someone who doesn't think it's wrong to teach Central Americans to kill each other.

Nothing that he said on Sunday night was new. His strong opinions of the world have not changed since he first electrified the right wing of his party 20 years ago with his defense of Barry Goldwater. The constant companionship of intractable problems has not deepened or aged him. He floats foolish notions without the slightest self-consciousness. He confidently expresses ideas on war and peace that go against the grain of the nation. He knows that the country considers him wrong, but strong.

And he does what he has to do to survive, even if it means contradicting himself and history. He has the true killer instinct, as he demonstrated when he meanly put the blame for the Beirut massacre on the ground commanders.

In his most reprehensible moment, he defended himself at the expense of Marine officers, who were following his orders and trying to carry out the murky mission he gave them. He forgot what he said last December when, accepting the blame himself, he declared that "The local commanders have already suffered quite enough."

But not enough, obviously, when he is a candidate pushed into a corner. Mondale was vigorously raising questions about the cause of the disaster. He seemed to be using material from Patrick Sloyan's devastating account in the current Nation magazine of the dispute within the White House over the wisdom of keeping the Marines at the vulnerable and exposed airport.

According to Sloyan, five days before the bombing, the Joint Chiefs of Staff and Secretary of Defense Caspar W. Weinberger begged the president to take the Marines out of danger. National security affairs adviser Robert C. McFarlane and Secretary of State George P. Shultz differed, and Weinberger's futile plea was formally removed from the record. Two hundred and forty-one U.S. servicemen died.

But in the debate, Reagan slyly switched the focus from the airport to the barracks, where the Marines were sleeping. It has been argued that if so many had not been in the building, fewer might have died. But that was beside the point.

"Yes, first of all, Mr. Mondale should know that the president did not order the Marines into the barracks. That was a command decision made by the commanders on the spot."

But the decision to keep the Marines at the airport was his.

Col. Timothy Geraghty, who warned McFarlane that the Marines would "get slaughtered" once the U.S. fired on any of the factions involved, deserves better of his commander-in-chief.

That was Reagan, the tough politician. Sunday night also gave us Reagan the dreamer, the dove who builds weapons to ensure their elimination. His presentation of the "Star Wars" program as a blow for world peace and human rights was strictly off the wall, made more so by his offer to share it with the "evil empire."

Mondale chose to hit on the improbability of Reagan sharing high-tech secrets with the Soviets rather than on the innate lunacy of the contrivance, a shield, not yet developed, that would spare the world the consequences of a nuclear attack.

Reagan did not trouble to explain how the "demonstration" for the Soviets would work, or more importantly, where it would be staged.

It was vintage Reagan: Negotiate with the Soviets tomorrow, about weapons that aren't off the drawing board, or maybe not even on it.

At least now, thanks to the League of Women Voters, the voters will go forth on Nov. 6 with their eyes wide open. They have seen Ronald Reagan plain. They have learned things that are arguably as important as the circles under Walter Mondale's eyes.