Ethel Merman's "got rhythm." Bernard Gittelson's got biorhythm.

Biorhythm has little to do with reducing the prospects of births, but everything to do with birth dates.

No self-respecting hunch player will make a bet in the future without consulting an athlete's physical, emotioanl and intellectual rhythms, if Gittelson can help it. And he can help it.

He says he already has sold a million copies of his first book, "Biorhythm: A Personal Science". Now he is zeroing in on atheletics with "Biorhythm Sports Forecasting."

For $9.95 a pop, his book will show you how to chart the "rhythms of life." He claims 80 per cent accuracy in diagnosing when a performer will be at his most productive level, or the reverse.

The publisher's motive is impugnable with a boxed blurb on the dust jacket that says, "Not intended for use by professional gamblers." That figures to have the same effect on sales ashaving a book banned in Boston once did.

And by the time the book browser turns to the flip side of the cover, he is informed. "This book is not designed to encourage gambling in any form. Its objective is to put an end to gambling losses." There's a difference?

Getting it on wilh Gittelson is a topical exercise.

Why did Bill Kilmer hit on six of eight passes against the Cleveland Browns and Joe Theismann on 16 of 24, while Mark Moseley barely scaped goat's horns by finally making good on his last of three goal attempts? he asked.

Simple Kilmer was born on Sept. 5 1939, and was up physically on Monday, although down emotionally and intellectually. Theismann, born Sept. 9. 1949, had physical and emotional pluses, although down intellectually.

Moseley born March 12, 1948, was passing through critical phases physically and intellectually and was low emotionally.

At first, George Allen might be alarmed to learn that on Dec. 17, when his Redskins play the Los Angeles Rams here in the last game of the season, the coach personalty will be in a three-cycle down curve.

Gittelson's book says of such a period: "The time is an interlude of clam - physical, emotional, intellectual. Strive to shake off the anxieties of the triple low. Relax with the thought that better days are not far away."

That should not be taken to mean that Redskins - or more particulary Allen - should abandon hopes of making the playoffs.

Gittelson's book cites Joe Namath's physical and intellectual cycles being negative when his New York Jets took the field against the highly favored Baltimore Colts in the Super Bowl game Jan. 12, 1969, but his emotional rythm was at its highest point and the Jets won, as he guaranteed publicly they would, 16-7.

Joe Louis prevailed under poor cycles in most of his bouts. He was very low intellectually and operating under double critical cycles otherwise for his bout with James J. Braddock, but won the title.

He was low physically and intellectually, and emotionally critical when he fought his only "grudge" bout, against Max Schmeling in a rematch, but knocked him out in the first round.

Muhammed Ali's chart show some of the same tendencies to flout "down" cycles.

Gittelson rationalized those instances by saying, "Some performers are at their best in a clutch. Most of baseball's no-hitters came on critical days for the pitchers, when they took extra chances. Ice skaters win on critical days; they take chances. For the average person, taking such a chance mean death."

What if a person determines from his biohythms that he performs badly in high cycles?

"Then you gave to go the opposite way, if your history is consistent."

Aug. 31 figures to be a worrisome for Billy Martin, manager of the New York Yankees. He will be in a physical low, a critical emotional phase and an intellectual low.

"This is a day for you to just take it as easy as possible," Gittelson's book tells persons in such a fix. "Avik hasty decisions and attempt to obtain as much rest as possible. You will find your system sapped by physical fatigue from the physical low.

"You will also feel uninspired as a result of your emotional rhythm being at a cross point. It is not a day to be feared as much as it is a day to be guided by caution. This is an accident-prone day."

O.J. Simpson's charts were remarkable for their apparent pertinence on Aug. 2, when he was excused from practice because he said he had blurred vision in his left eye: "Though you may feel spent physically, your emotions are in plus. This should provide some assistance to the physical 'critical' condition you are in.

"Awareness is required for you to take steps to adjust to and to overcome your intellectual low. This is an accident-prone day."

On Aug. 8, the day his eyes were examined in Johns Hopkins University medical center, he was in a triple joy, with the advice from the book, available to George Allen, applying. He was given clearance to practice again.

Author Gittelson in a cram course, notes, 'These studies concerned themselves with a compound of two Greek words - bios and rhythmos - which mean 'life' and a 'perodic beat."

He points out that there is a 23-day physical rhythm, a 28-day emotional one, and a 33-day intellectual pattern.

A single critical day, when the cycle crosses the baseline between plus or minus, takes place about six times a month; a double critical day about six times a year, and a triple once a year.

On physically critical day, there is less resistance to disease. Strength, speed, and resistance are at low points.

Emotionally critical days make the individual open to self-inflicated harm, to violent argument, to behaving in a disagreeable manner.

There is a down spiral for anaylsis and decision-making when the intellectually critical days take place. This also is a time when accidents occur because of negligence, or a time of "human error."

If the book is not totally reliable for gamblers, it can serve as an ice-breaker at parties. A woman does not have to tell her age. She can look up a code for it in the book and then let the life of the party try to predict her moods.