THE BELL FOR the fourth period brought Susan out the side door. She was dressed in clogs and jeans, a light sweater and oversized sunglasses. She walked quickly across the street, her clogs making this scraping sound, and she went right up to a friend. She dipped a hand into the friend's jacket pocket, took out a cigarette and lit it. Then Susan, who is 17 years old, did what the other did. She smoked. They all agreed they were killing themselves.

All around were the kids of a Washington high school. They were sitting on the steps of a school and they were across the street by the flagpole with no flag and a lot of them were nearby in a field of new and very green grass. They were smoking. Some of the boys were smoking but more of the girs, so many more that they said they didn't know any boys who smoked-just girls. It has become a sex-linked trait, like color-blindness or something.

In the speeches of HEW Secretary Joseph Califano, we learn that 26.2 percent of all girls Susan's age smoke. This is up from 18.6 in 1968 and it means that for the first time in history, there are more women smokers in an age group than there are men. In fact, it means that in every age group but older teen-age girls, smoking is on the decrease. Only among girsl 17 and 18 is smoking increasing. It's a puzzle. They are, after all, old enough to know better.

"I know it's stupid," said a girl named Debby. She was dressed in dungarees and an orange blouse and her face was sprinkled with freckles. "You get this cough and it's bad for you. You wake up in the morning and you cough." She grabbed herself by the throat and made a gagging sound. Her friend, Jean laughed. Her friend Jean smoked, too.

"I started three years ago," she said. "I was 15. It was a cool thing to do." She shrugged her shoulders as if even she didn't understand it anymore. "Now it's a habit." That anyone can understand.

An unmarked police car, so plain it was obvious, stopped up the street. Two men inside looked around the area. All they saw was kids smoking. If they were smoking pot, they could be arrested. If they were smoking cigarettes, nothing happens. Pot can get you high. Tobacco can kill you. If you're a girl and pregnant, it can harm your baby. Susan and the other girls know all that. They have seen the films. They have read the booklets. They have had their parents yell at them. They smoke anyway.

"It's just something you do," Susan said. "I don't know why. You get all tense and you need to relax. A cigarette relaxes you."

"But not if you don't already smoke," I said. "It only relaxes you if you already have the habit."

Susan shrugged her argeement. She looked around and then at me. Behind her large glasses, her skin was blotched and pimpled-a skin I know so well. I used to have it-every morning a different face for the world. "Not a lot of the boys smoke," Susan said. "Nearly all the girls do." She paused and looked down. "Not all of the girls," she said correcting herself. She named some who don't.

"Who are they?"

"The smart ones," someone said.

"They're the ones who get good grades," Susan said. "They don't smoke."

Pretty soon it was me and Susan-the two of us doing most of the talking. The others listened as we talked about why girls their age smoked so heavily. As we talked, Susan swung her legs faster and faster and she said something about how smoking had to do with not liking yourself ver much-with being unhappy or something. It was hard to say just what.

"You know you don't get good grades and you're not doing so well in school and you have trouble with a parent and you might as well smoke." Her legs were moving faster now. "You know what I mean?"

Maybe. All I know is that when I was a teen-age boy the biggest sucker going was a teen-age girl. They fell in love with movie stars and swooned for singers with greasy hair and you could tell them anything and they believed it. You lied to them all the time and told them what they wanted to hear and that, in a way, is what the cigarette companies are doing now. They show handsome people in the ads, happy people in the ads-ads that somehow make it terrific to smoke.

Susan sat on the wall, her legs going a mile a minute. She was nervous now and lit another cigarette. She looked at the cigarette and laughed. She knew what she was doing but then she thought she was doing something else. It's only a guess, but somehow she thought smoking enhanced her looks. It's an old routine and the cigarette companies do it very well.

It's called telling a plain girl an ugly lie.