Today is a day for squares -- 9/9/81 -- the first day since Aug. 8, 1964, in which the number of the year is the square of both the day and the month. It has been happening in this century since the first day thereof, which was Jan. 1, 1901, but less and less frequently as the decades roll along.

It was not much of a jump to Feb. 2, 1904, and only a bit more of a stretch to March 3, 1909. But the square days don't seem to come around the way they used to; today is only the second since July 7, 1949. Since the median age of the American population is only 30, most of us have seen only two such days. And we will not see another in this century -- unless you count Oct. 10, 2000, which is doubly problematic, first, because 00 doesn't look like the square of 10, and second, because some people have trouble accepting the year 2000 as the end of the 20th century (which it is) rather than the beginning of the 21st.

Straight days, in which the numbers line up in a row, happen even less often, at least for purists who limit themselves to celebrating five-digit straight days. They couldn't even begin happening this century until Jan. 23, 1945, by which time square days had almost petered out, but the next one comes fast: Dec. 3 of that same year. After that they become impossible, since the year 1956 lacked a Feb. 34. Don't talk to me about such skimpy straights as Jan. 2, 1903, or Feb. 3, 1904; they are too common, too unexceptional to deserve any notice. One might have quaffed a beer to celebrate Jan. 2, 1934, since beer-quaffing had been legalized only a month earlier. But either of the days in 1945 would have been a champagne day -- for those whose parents would have allowed it. At the time, of course, it would have been hard to get the imported stuff -- the war, you know.

Four-of-a-kind days begin with Jan. 1, 1911, and continue through Sept. 9, 1999, which sounds rather like a German speaker in a very negative mood if you do it all in numerals. They come with a rather boring, clockwork regularity 11 years, one month and one day after the last. By the way, 1911 enjoyed one day that was unique: Nov. 11, the only six-of-a-kind. It also has more five-of-a-kinds than any other year: Jan. 11 and Nov. 1. The only other five-of-a-kind is Feb. 22, 1922.

The square days seem clearly worth noticing, and this one in particular, since it is (according to the most widely accepted consensus) the last we shall see in this millennium. Your attention is therefore directed to Ron Gordon, a teacher at Carlmont High School in Belmont, Calif., apparently the only man in the United States who is trying to organize a nationwide observance. His announcement:

"Our high school has challenged high schools across the country to see who can form the biggest square root sign -- like a marching band on a football field. The students pledge to give their undivided attention in a calculated effort and to practice it times and times again. Once they've done their quotient of work, they may ask to be excused for the remainder of the day. The answer: Stay and check your work. It figures."

Reached by telephone, Gordon is slightly more communicative. He confesses that he thought of getting T-shirts and buttons for participants saying "I got my root squared on 9/9/81," but decided that some people might see off-color overtones beyond the pure mathematics of the statement. (Maybe it has different connotations in California.)

He is not sure what kind of response he may have. It was hard to get the word around, he said, "today being the first day of class."

He has a friend who is celebrating a birthday today and has suggested that people should cut up turnips, carrots and potatoes into equilateral quadrangles "so that they could give her a bunch of square roots." But he does not know whether anyone has done anything about it. He is also looking for a grandparent who is 81 today and has twin grandchildren or great-grandchildren age 9 to receive a "golden root" award, but he doesn't know what the award might be. "Maybe a carrot?" he offered. "Or perhaps we could get a dentist to do a free root canal."

A high-school teacher so obsessed with roots (not in the Alex Haley sense) is, of course, a mathematics teacher? "As a matter of fact, no," Gordon answers. "I teach biology."