IT FINALLY CAME. The call I've been worried I wouldn't get, and the call I've been dreading. It came a couple of weeks ago to my parents' home in Arlington. Someone named Mary White was looking for me. She said she had gone to high school with me and was trying to find me to tell me about a class reunion being planned.

Well, the message got passed along to me, and even though I couldn't remember anyone named Mary White, I called her. It turns out that she isn't really Mary White at all. She is really Mary Chaconas, who married someone named Jim White 17 years ago, and now has five children and lives in Falls Church. And it turns out that Mary Chaconas, Washington-Lee High School class of 1961, is helping to put together the class's 20th reunion. Why she called, I have no idea. It can't possibly be 20 years since I got out of high school. Not 20.

Only 19. The reunion, it turns out, is a year off, amd maybe then I'll be able to handle the idea of 20 years better than I can handle the idea of 19 years now. But that is not the point. The prospect of an impending reunion has brought to mind something I have never understood about reunions. For years I've heard stories about people getting together after 20 years and discovering that the Most Likely to Succeed dropped off the face of the earth while the guy no one ever heard of turns out to be a space hero. It happened again on TV the other night during the movie "Reunion." No one ever explains this phenomenon, but that's not what intrigued me.

What I want to know is, how on earth do they ever find anybody? This is not exactly Pocatello, Idaho, around here. People left their homes in Arlington to go away to college and maybe their parents moved, and how is anyone going to find them? As for the women, 20 years ago everyone who got married took their husband's name. How would anyone ever find me? If Mary White weren't busy trying to find people, how on earth would anyone know she was really Mary Chaconas?

It ain't easy, say Mary White, Jody Gavin and Sue Dungan, who are now trying to locate some 750 people. They want to put them on a mailing list to tell them the details of the reunion, which is now scheduled for the Columbus Day weekend of 1981. They are planning a football game and a dance and maybe a brunch. So far, the search committee has located about 250 people, from New York to Florida, and Virginia to Alaska, not to mention Switzerland, Germany, Italy and Norway, which is not bad for a month's work.

They contacted the school and found out, understandably enough, that it had not kept school records of people's lives after high school. So they started going through the yearbook and then looking up names in the phone book, hoping to locate parents or relatives or the graduates themselves who are still in the area. They found some people who couldn't remember the year they graduated, and one person who said she didn't want any part of it, and one child who said his father had gone to the high school that year but never mentioned that his mother had, too.

"One man we talked to for about five minutes," says Mary White. "He said no, there was no one in that family by that name. So I told him about what age the man would have been and he said no, there was no one by that name, no one in the area by that name. Then just as I was about to hang up, he remembered and said, 'no, wait, that's my son.'"

They found that several of the graduates have died. They found that practically everyone they have reached so far is divorced or in a second marriage. They found that some young men who were too short in high school have finally grown while others have become bald.

"Of course," says Susan Dungan, mother of four. "We all look the same."

Of course we do. At least Mary, who was the one I knew best in junior high as well as in high school, looks the same. She has the same blonde hair I always envied, the same extroverted personality. She does seem a little fuller in the middle than I recall, but that's understandable, I suppose. She's had five children, and she must have been 18 when she graduated, so she can't -- as she said herself -- be that far from 40. She says I look about the same, which must mean that I haven't gotten lines on my face or developed around the middle. But then I probably won't for awhile, and that's understandable, too.

Would you believe I graduated from high school when I was 12?