- Step on a crack, break your mother's back.

Third grade? Earlier? Whatever the age - and this particular rhyme is ex cruciatingly familiar by the time a youngster enters the early years of grade school - superstitions affect the lives of individuals worldwide.Friday the 13th. The very mention of this day evokes caution in many people and in some cases causes outright fear. Why? Why Friday and why 13?

Why is it bad luck to walk under a ladder? Why is one doomed if a black cat crosses his path? Why must one suf fer through seven years of misery if he breaks a mirror?

I thought that spilling salt was detri mental only if it happened unknowingly on your hamburger. Others, however, think it's better to knock on wood after such a spill than to fry another slab of meat. Why? Some cooks blame an un successful cake on the inconsistency of the batter. Why do some blame personal disaster on that same inconsistency?

Spirits, that's why. Demons. Its roots ancient, superstition springs from the belief that strange or mysterious events were caused by good or evil forces. The fortunate - or perhaps unfortunate - had the power to control such events.

That raises a question: Today, does this mean these gifted individuals in clude those we know as presidents, prime ministers and premiers? After all, haven't we all seen some strange events resulting from the powers of these lead ers that simply cannot be explained sci entifically?

Ah yes, science, the forgotten field. While this seemingly forgotten art of scientific thinking helps to dissolve su perstitious leanings, people today hold onto these beliefs. And, though there has been some speculation that superstitious convictions are strongest in the relative ly uneducated, educated folk, too, go through their daily rituals determined not to step on a sidewalk crack. Non-be lievers simply conform because it seems the safer thing to do. Why risk your mother's back if you don't have to?

Did you ever watch a baseball man ager take that long, unenviable walk to pull his pitcher from a game? Most opt for a small skip over the baseline. Why? It would seem the walk itself is an indication that his luck has all but soured already.

Managers and sports figures in gen eral are a strange breed. A hitter in a slump won't shave until he comes out of it. But honestly, looking like a ZZ Top refugee won't help anyone hit better, whether you're Wade Boggs or Whiffle Ball Willie.

Superstition or not, though, at least one baseball tradition has had an al most scary relationship with Wall Street. Billy Martin, well chronicled and in the news again this week for his - ahem - volatility, was named last fall as manager of the New York Yankees. The announcement not only marked the Hall of Famer's fifth stint with the Yan kees but was quickly followed by - you guessed it, sports fans - a fall in the value of stocks.

Five times Mr. Martin was named manager of the Yankees, five times stocks have plummeted. George Stein brenner, principal owner of the team, named his new field chief just before Black Monday. Crazy coincidence, isn't it? Or is it? Do us all a favor, Billy, and lead the Yanks to a pennant or two. And, George, be patient, real patient.

Several superstitions relate to bibli cal passages. A horseshoe, prongs up over a door, supposedly wards off evil spirits and brings good luck. Of course, the shoe must be hung by three nails, struck three times with a hammer. One explanation for this obsession with the numeral three is that each nail and blow represents a part of the Almighty. One for the Father, one for the Son and one for the Holy Spirit.

In addition, some trace the belief that Friday the 13th itself is deemed unlucky to the fact that Jesus was crucified on a Friday and 13 people attended the Last Supper. Of course luck - good and bad - and superstition in general, fly in the face of faith.

So, what about this (dis)illusion of Friday the 13th? Are demons, spirits and slashers aroused as Hollywood leads us to believe? Can Jason, the crazed slash er in the movie Friday the 13th, and others like him who give this day such a bad name be stopped? Perhaps. In fact, it may be time for a call to go out to one Sly Stallone, who played the prize fighter Rocky Balboa in a series of movies. What do ya say, Rock, is there a future for a Jason-Balboa showdown? Maybe Friday the 13th Part XIII: The Incarnation of Rocky.