A presidential candidate needs the characteristics of an astronaut and a sledgehammer. An astronaut because running for office requires an abnormal combinaton of daring and attention to detail. A sledgehammer because running requires an almost inhuman obdurateness.

John Glenn, who obviously is thinking of running, acquired the attributes of an astronaut by becoming one. Twenty years ago on Feb. 20, 1962, he flew around the Earth and, as is said, into the hearts of his countrymen. Whether or not he has attributes that would cause the sledgehammer to sit up and say "That's my boy!" remains to be seen.

It is Broder's Law (named after its author, columnist David Broder, the Newton of the physics of politics) that anyone who desires to run for president, especially now that there seem to be more state primaries than there are states, reveals by his desire to run that he is too loony to be entrusted with the office. Broder's premise is that the desire to run for president may be public-spirited, but certainly is peculiar. So Broder's Law leads us to the Glenn Paradox: Glenn's charm is that he is almost abnormally normal.

A politician's first task is to solve his "name-recognition" problem. No one ever solved that problem more expeditiously than Glenn did with his short flight -- America's first orbital flight. It made him emblematic of the zip, pep, vigor and general can-do spirit of the Kennedy years.

The secret of American politics generally is to be, or at least to be seen to be, middling: in the middle of the road, and in the middle of the general range of human virtues and aspirations. And it does not hurt to come from the middle of the country, which Ohio can claim to be, symbolically if not geographically.

Beginning with the ninth president (William H. Harrison in 1840) through the 29th (Warren G. Harding), six presidents (and three vice presidents) were elected from Ohio. Two other presidents were born there. Harding caused the nation to put a moratorium on having Ohio presidents, a moratorium that not even Robert Taft could get the country to break.

Ohio is where the Middle West begins, yet it is a seaport for ocean-going shipping. It combines a strong agricultural economy with six major industrial centers, producing glass, rubber, steel -- all the things that make automobiles and make Ohio so vulnerable to the economic problems of the old "smokestack" industries. Glenn represents the "smokestack" Democratic Party, a party grounded in the issues and constituencies of classic American industrialism. It is not clear that full restoration of that America of the smokestacks should be an American aspiration.

But Glenn also represents, temporarily and politically, the tendency within the Democratic Party that was the dominant tendency when he orbited the Earth. That tendency has been in eclipse for 15 years, and the restoration of it to predominance within the party is to be desired, and not just by Democrats.

That is, Glenn is a Democrat in the Roosevelt-Truman-Kennedy-Johnson tradition -- a tradition exemplified by Pat Moynihan, Henry Jackson, Sam Nunn and Fritz Hollings among Glenn's Senate colleagues. He sees no incompatibility between strong defense and strong social policies, no conflict between liberal social values and a nationalist, anti-communist foreign policy. This kind of Democrat, although representing a clear majority of this party's rank and file, has not represented the party at the national level since the decisive event of the party's modern history: the McGovernite takeover in '72. Glenn, a Marine pilot, is a graduate of the Naval Academy. He takes defense policy seriously enough to have organized an after-hours bipartisan study group that meets periodically for dinner and discussion.

But even the best ideas depend for their effectiveness on some forensic competence. As a public speaker, Glenn is a bit like Cream of Wheat: nourishing but not exciting. Still, in 1980, when Democratic senators were falling like leaves in an autumn gale, Ohioans did not just re-elect Glenn; they conferred upon him a second term virtually by acclamation. He got 69 percent of the Ohio vote while Ronald Reagan was getting 52 percent.

Of course, Americans do not look at presidential candidates and Senate candidates in the same way. They seem to want their Senate candidates to be just folks, but they want their presidential candidates to be rather more. Americans loved Jerry Ford, but did not elect him.

Since 1804, only seven presidents have won the White House without winning Ohio.In this century, only two presidents (FDR, in 1944, and JFK) have done so. No Republicans have. That should be encouraging to this man of the middle, from the middle of Ohio. He is from New Concord, down the road apiece from the home of two other. Ohio pioneers of flight, Wilbur and Orville Wright.