A group of Alexandria youths has successfully persuaded City Council members not to ban bicycles and skateboards from Market Square.

But the council did pass an ordinance that prohibits Mopeds and other motor vehicles as well as graffiti from showing up on the bricks and stonework of the city's central gathering spot. Violaters of the new law can be fined up to $100.

Between 20 and 25 teen-agers and younger children walked into the council meeting last Saturday and quietly took seats in the back of the room after filling out forms permitting them to speak at the public hearing.

Colin St. Clair, 14, who graduated from George Washington Junior High School this week, said his father had told him about the proposed ban in May. St. Clair said that word of the ban spread quickly among all the youths who congregate at Market Square.

"I'm happy we get to stay here. I felt relieved," said St. Clair after he and his friends spoke before the council.

Many of the cyclists, called "BMXers" after the BMX style of bicycle (which stands for "bicycle motor cross,") use these bikes with 20-inch wheels to ride down steps, jump curbs and perform stunts called "wheel hops." To do a hop, the rider balances the bike on its front wheel and bounces on the tire as if on a pogo stick.

"It's the perfect place. People enjoy watching us. Tourists take pictures a lot," said St. Clair, who comes to the square every day. "I think that other people should be able to enjoy the square, too."

"I think that people should keep this place cleaner," said St. Clair, pointing to a brown paper bag and empty beer can propped up next to a graffiti-marked stone. "I hope other people don't mess it up."

Kristina Hohlweg, 15, said that the young people who come to Market Square have no place else to go. "You can't go to a parking lot. It's not safe with cars going in and out."

Hohlweg, also a recent graduate of George Washington Junior High School, said she was elated after the council decided against banning bicycles and skateboards. "It shows that you can do something if you try. They did listen to us," Hohlweg said.

On the recommendation of Mayor Charles Beatley, two older members of the youthful group that frequents Market Square have agreed to act as deputies to assure that no one defaces the area with graffiti.

John Jett, deputy director of Alexandria's Department of General Services, which keeps up Market Square, said the city will soon pay about $4,500 to grind away the graffiti on the hundreds of feet of limestone that line the square's fountain and gardens.

But not all council members were persuaded by the arguments of the young.

Vice Mayor Patricia S. Ticer and Councilwoman Margaret B. Inman wanted the ban to include bicycles and skateboards.

"I think it really does detract from other people's rights. I think it's dangerous for people walking through the park," Ticer said. The vice mayor also questioned whether the teen-age deputies could stop older and physically bigger persons from doing as they please.

Citizens' complaints about loud radio music, cyclists darting in and out of crowds on the square, and skateboarders using the square as a jumping ramp prompted the council to upgrade the former park regulation to an ordinance that will now be enforced by the police department, according to assistant city attorney Stuart J. Tenhoor.

The proposed ordinance would also have stopped people from bringing portable radio and tape decks, but Tenhoor recommended against this portion because it may have interfered with the radio players' constitutional rights, Tenhoor said. "I think there were some risks with the First Amendment. You have to have strong reason for taking that kind of step," Tenhoor said.

There is a noise ordinance in Alexandria that says it is unlawful for anyone to make noise that annoys, disturbs or injures a person. It also restricts noise to lower decibel levels between 11 p.m. and 7 a.m.