More than 100 teen-agers, many of whom are parents, met at the Washington Convention Center yesterday to discuss sex and teen-age pregnancy and to offer city and federal legislators, school officials and parents suggestions on how to decrease teen-age pregnancies.

Discussions at the day-long conference were often laced with stories of the hardships of being a teen-age mother.

Loretta King, a District student, introduced herself by saying, "I have two kids and I go to Cardozo Senior High School. I told my mom if I'm 35 when I do it, I'm going to finish school. It's hard. I dropped out in ninth grade for the first child and I'm still trying to finish the 10th grade. It's hard. It's real hard."

"Understand -- what you say here today will affect the lives of many other people; I hope you speak frankly," Eunice Kennedy Shriver, executive vice president of the Joseph P. Kennedy Jr. Foundation, told the youths at the conference.

The foundation's "Community of Caring," a 10-year-old counseling program for adolescents, sponsored the "Teen Forum On Love, Sex, Parenthood," which was attended by 60 D.C. area youths and teen-agers from Texas, New York, Oklahoma, New Mexico and Pennsylvania.

In 1984 in the District, there were 51.4 births per 1,000 teen-age girls. While nationally the rate of births to teen-agers has been dropping, about 1 million teen-agers become pregnant each year and the percentage of teen-age mothers who are unmarried has more than tripled in 25 years.

"The Kennedy foundation believes teens themselves have a lot to offer as far as a solution to teen pregnancy," George A. Zitnay, program director, explained.

The teens had their say when they broke into smaller groups of about 20 to look at and discuss film clips that included segments from the controversial CBS special, "The Vanishing Family."

Asked to answer the question: "Who am I?" Patricia Smith of New York told her group: "I have a beautiful son who will be 6 months old on the 6th. I'm in 10th grade. I live in Brooklyn, N.Y. I've lived there all my life. I'm striving to get out."

Later, she said, boldly, "A lot of people look down on black teens, but I feel I'm a good mother to my son."

In an attempt to get a cross-section of teens, the foundation staff invited to the forum teen parents, teens without children, student leaders and dropouts.

When Pansy Doles of Brooklyn told the group she was 17 and the mother of three, someone asked her why a teen-ager, after having one child out of wedlock, would have a second child.

"The second time I had twins. They were a mistake," said Doles. "But I was married at the time and that made it a little better. It's hard, though. Just hard. No one knows how hard it is to raise three children alone," added Doles, who is separated from her husband.

At the end of the forum, one young man told the adults: "If we are the future, then train us to be the future." The students overwhelmingly supported school-based health clinics and suggested better sex education be included in their school curriculums, including more about the meaning of love and what makes relationships work.