IF HE WERE making up his mind last week, Ronald Reagan probably would have said yes to running again. Sure, he had Lebanon on his plate, but when does a politician have the peaks of personal satisfaction he is currently scaling?

Here he is, the onetime "right-wing kook" with the whole world, including Nicaragua, agreeing with him that the Soviets acted like Genghis Khan in the Korean airline incident.

The right wing of his party, which alone squawked at his statesmanlike restraint on sanctions, was assuaged by his offhand suggestion that we can get the United Nations out of the United States for at least part of the time. The Rev. Jerry Falwell helpfully pointed out that the conservatives will have nowhere else to go in 1984.

Reagan's pollster, Richard Wirthlin, brought him the gladsome news that his 1980 support from Democratic blue collars was no fluke. His crucial margin with them has, in fact, increased slightly.

Even in Johnstown, Pa., which has the highest unemployment rate in the country, the jobless forgive him. "He's doing the best he can," they say, in a manner calculated to baffle and madden Democrats.

In liberal Massachusetts, Wirthlin found, Reagan runs ahead of Democratic front-runner Fritz Mondale and orbiting John Glenn. Bay State women are still what pollsters call "lagging indicators," but the slack is more than taken up by men, who like the president now more than ever. So much, it seems, for the gender gap.

Perhaps the most astonishing finding which Wirthlin shared with a Washington Journalism Center seminar was that Reagan, who slams Washington and all its works every chance he gets, and often seems to forget that he is in charge of it, has softened Americans' attitude towards the federal government. They are "less cynical and pessimistic" today than when he took office.

What he has going for him more than anything else, though, is his seemingly indestructible nice guy image. As president, Reagan has instituted policies that are hard on people, that are even mean. He shamelessly chooses guns over butter. While ever striving to permit the rich to keep more of their money, he has tried to make sure that the poor don't get too much.

His administration instituted reviews of the eligibility of mentally and physically handicapped recipients of Supplemental Security Income. It is a harrowing process that has shortened some lives. He has done nothing to stop it.

Abroad, he has subsidized the killing of Nicaraguan peasants, who have done nothing to him, or us, except live in a country with a government he doesn't like. He has not hesitated to impugn the patriotism and intelligence of people who want to stop his mammoth buildup of nuclear arms.

He has surrounded himself with appointees whose taste and ethics would impel a more sensitive chief executive to call for beheadings. Reagan is either tolerant of, or amused by, their actions. He may publicly rap the secretary of interior, who regularly slanders large groups of citizenry with a smirk that suggests he knows just what he is doing, but James Watt remains firmly in place.

Officials say outrageous and dangerous things, from the National Security Council aide who said the Russians better shape up or expect war, to a high Defense Department official, who said that with enough shovels, we could survive a nuclear war. Reagan shrugs and says they are "personal views."

Just recently, a deputy defense secretary declared that we seek "a military victory" in Central America. Reagan has insisted we want negotiations, but his press secretary stoutly defends the "victory" statement.

At Reagan's press conferences, he routinely makes gaffes and misstatements. He says things that are inconsistent or just plain wrong. His staff stoically cleans up after him. He doesn't seem bothered. He knows what happens to compulsively well- informed chief executives -- like Jimmy Carter and Lyndon Johnson. He may know, from a source hidden from the rest of us, that the public is more at ease with a non-perfectionist, no-sweat, average-guy kind of presidency, in which the real care is expended on the "photo opportunity."

Gov. John Sununu of New Hampshire, who, like other Republicans, is looking forward to Reagan's re-election campaign, thinks that Reagan's obvious enjoyment of the office has given the electorate warm feelings about him.

"They don't want to feel that they have punished somebody by electing him president."

Reagan's age, 72, Wirthlin finds, is no more on the voters' minds than it was in 1980, which is to say not at all.

The Democrats can't make an issue of his luck and his popularity. But those are what make it most likely he will run again and what make it so difficult to beat him.