What qualities should a president have? In essence, this was the question posed by Stephen Hess of the Brookings Institution. He asked political journalists to rate the presidential candidates on 10 criteria. The Republicans who did best were Sen. Bob Dole and Rep. Jack Kemp. The Democrats were Bruce Babbitt, Jesse Jackson and Sen. Albert Gore. For the candidates selected, a version of an old New York expression comes to mind: the honor plus a nickel (now $1) will get them on the subway.

But the presidential nomination is a different matter. For that, it's instructive to recall a candidate from yesteryear -- Ronald Reagan. For obvious reasons, Hess did not list him as a candidate. Had he, the outcome would have been telling. It's hard to believe the president would have been rated high on intelligence, stamina, executive talents or expert knowledge.

After the Iran-contra affair, Reagan might even have been downgraded on honesty and maybe even on what Hess calls a sense of history. And yet, in strictly political terms, Reagan's has been a successful presidency. In fact, if Reagan were eligible for a third term (and not approaching 77), he might win again. There's probably not a Democrat in the field who could beat him.

Why? One answer has to do with a category Hess did not include: luck. There's no doubt that Reagan is a lucky guy. He was lucky enough to be born handsome and hearty. He was lucky enough to walk into a Hollywood career. He was lucky enough to survive an assassination attempt that -- another minute, another inch -- might well have been fatal. And, finally, he enjoys astounding good health for a man his age. The ultimate luck is to be born with good genes.

In his presidency, also, Reagan has been lucky. Take inflation. Reagan claims to have tamed it and, indeed, the numbers back him up. In 1980, the annual inflation rate was 13.5 percent. It's now 4.7. But the price of oil -- key to the inflation rate -- has dropped too. When Reagan came into office, the official OPEC price was $41 a barrel. It's now 18 -- and sinking. Did Reagan have anything to do with a decline in oil prices that contributed so much to the downturn in inflation? Not on your life. OPEC simply fell apart. That's luck.

Or consider U.S.-Soviet relations. Reagan claims that his arms buildup brought Mikhail Gorbachev to the bargaining table. Maybe. But while Reagan was building up the military, the Soviet Union was having almost a leader a year. Three Soviet leaders died during Reagan's first term. That meant, among other things, that our prime adversary was going though an unstable, confusing period. It's doubtful it could have responded to a Reagan initiative even if it had wanted to. Once again, Reagan was lucky.

Of course, a person tends to make his or her own good fortune. If, in fact, Reagan's policy toward the Soviet Union was sound, it was only a matter of time until a Russian leader cried uncle in the arms race. But luck is also a special, mysterious quality some people seem to have. By now, the American people know that Reagan is lucky. Since he's our president, Reagan's luck is our own. Like someone betting on a hot craps player, we are only too glad to go along for the ride -- even when, as with Reagan's incredible budget deficits, we know we have to run out of gas.

The quality of luck is special, rare and yet real. Jimmy Carter had enough of it to win an election in 1976 but not enough to sustain his presidency. Nothing exemplifies that more than the seizing of American hostages in Iran and the short-term success of OPEC during the Carter administration. And nothing exemplified Reagan's luck more than the release of the hostages on his inauguration day -- and the subsequent collapse of OPEC. The president seemed to be playing with a hot deck.

Luck is one of the ingredients that goes into the mix we call charisma. Reagan has that -- a star quality that's attractive and draws others to him. Coupled with his other qualities -- a perceived value system, a sense of his own worth, an innate optimism and decency -- they transcend the neat categories academics and journalists consider presidential.

Politics, like love, has its indefinable qualities. Both parties boast candidates who in almost every one of Hess' categories rate higher than the president -- Democrats highest of all. But for all their talent, intellect and expertise, the one quality they might not have is the one that might matter the most in the post-Reagan years. It would be just our luck if Reagan took his with him.