Police had barricaded the parking lot at the Northern Virginia Women's Medical Center when the blue Chevy van edged past the 500 demonstrators yesterday morning and was stopped.

"Do you have a reason to be here?" asked the Fairfax County policeman, one of 36 officers at the clinic carrying riot sticks.

"Yeah," replied Walter, 16, looking over at his 19-year-old girlfriend Norma.

"What?"

"An abortion," said Walter, putting his van in gear and pulling away from the demonstrators who were there to protest with their children, their red roses, and a Catholic bishop.

Norma, a bookkeeper who grew up going to a Presbyterian church and Sunday school almost every week, had an appointment yesterday for her second abortion this year. She thought the first one was wrong; she thinks a second abortion is wrong.

But she said she wanted the abortion because she and Walter cannot afford a baby, an apartment, and the trappings of married life.

The waiting room at the clinic has bright yellow walls, green and red plastic chairs and on one yellow wall is a framed first page of the 1972 Supreme Court ruling that gives Norma the right to an abortion on demand up to the third trimester, sixth month, of her pregnancy.

Outside, beyond the blocked-off parking lot, anti-abortion protesters with placards that said "Respect Life," sang about God and America, decrying the ruling they say sanctions murder.

Inside, on a green plastic chair, Norma picked at her fingers, twirled her brown hair in little knots and waited for her pre-operation counseling session. Walter, a high school dropout and an auto mechanic, sat beside her and kissed her twice.

Policemen paced outside the waiting room, occasionally stepping inside to ask the receptionist if any protesters had somehow managed to sneak inside. Several women had called the clinic earlier in the week saying that some antiabortion demonstrators planned to make appointments for an abortion and would create a ruckus instde the building.

Norma, a tall, thin woman with green eyes, said the policemen made her nervous.

When Norma discovered last month that she was pregnant, she and Walter were pleased.

"Oh, we were happy," said Walter, who has dark brown hair and a baby face. "We were going to get married and live together. We had an apartment planned and everything. It all changed because of our bank account. We'd always be in a hole. If I ever got sick, we'd be out of luck."

Walter makes about $175 a week fixing cars; Norma makes $112. With inflation and the high cost of apartments in the Washington area, Norma and Walter said that a baby is too expensive.

The high cost of babies was made clear to Walter and Norma by Walter's mother. She wrote them a five-page letter last week, discussing the costs of hospitals, diapers, baby clothes, school and the unsteady income of her son.

The letter changed Walter's mind about marriage, and he set out to change Norma's mind about abortion.

Norma's first abortion was on Feb. 5. She says she then came to the clinic, which performs 350 abortions a month, and has been the site of years of protests, expecting "they were going to tear me up."

The operation went smoothly, taking less than 15 minutes. But Norma said she spent the next three months feeling guilty. She was not using any birth control method when she became pregnant the first time. This time she had run out of the birth control pills a gynecologist had given her.

"I'd always told my father (a retired CIA electrical engineer) that I'm not stupid enough to ever need an abortion, but I made the same mistake twice," said Norma.

Walter persuaded his girlfriend, whom he says he loves and will continue to see after the abortion, to come into the clinic for the operation. But he says he just couldn't persuade her to think of the operation as anything but "murder."

"I don't like to think about it actually," said Norma. "They are fighting about it now in the courts anyway, trying to figure out whether it is life or not."

Norma, who graduated from high school last year, said that if she thought about abortion "a lot" she would think it was murder. "But I don't think that way," she said.

Norma said she allowed a reporter to accompany her to the clinic yesterday to show the antiabortion protesters that a decision to have the operation is not easy, that it is not a clear choice of right or wrong.

"A lot of them (the protesters) think we just go in here and have the abortion, that it doesn't bother us. But it does," she said.

The clinic's head nurse, Stephanie Bulik, called Norma in for her counseling session at 10 a.m. Norma walked out of the waiting room, down a brightly lit hallway and past posters that said "You're in good company if you're one of over 4 million women to have medically safe abortions in the last four years."

Walter went for a drive while Norma talked to the nurse. On his way to the van he walked past the window of the office where Norma and the nurse were talking. Norma waved, Walter waved back and the nurse said Walter was "cute, like a basketball player."

Bulik, a 27-year-old nurse who chain-smoked cigarettes as she spoke, told Norma that she would explain the upcoming operation completely, even though the young woman had been through it all before. But first Bulik asked:

"Why did you stop taking the pills?"

Norma's answer was vague and the nurse said abortion was not a preferred method of birth control. "Before you leave today, I want to talk to you constructively about a really good birth control method," Bulik said.

The nurse asked Norma how she felt when she discovered she was pregnant. Norma explained that her happiness ended when she realized -- partly because of the letter from her boyfriend's mother -- that she couldn't afford a baby.

After getting assurances that the abortion was what Norma wanted, Bulik explained in explicit, clinical detail the discomfort the operation would cause.

Bulik then warned Norma about possible complications from the abortion, including perforation of the uterus, infection, hemorrhaging, incomplete abortion and continued pregnancy. The nurse said Norma should realize these problems were "possible," although unlikely.

Norma left the room and moved to another with an examination table. She removed her clothes, put them in a plastic bag, pulled on a hospital gown and mounted a table for a pelvic examination.

The doctor entered the room and, after a brief examination, announced he couldn't perform the operation at the clinic, since Norma was between 13 and 14 weeks pregnant and the clinic performs abortions only up to the 12th week.

The protesters outside had sung their songs and left when Walter took Norma and went home. Norma said she planned to make reservations for an abortion at Washington Medical Center and that she would try not to think about what she was facing, until she goes to the hospital.