Sidewalks are for pedestrians and streets are for bikes, according to a Cambridge ordinance that will ban bicycling on all sidewalks in Harvard Square beginning Friday.

Cambridge police said they will "strictly enforce" the ordinance, which carries fines of $20 per violation and has drawn the ire of several Quad residents.

During May, two officers on bicycles will be patrolling the Square and issuing verbal warnings. They will begin handing out tickets around June 1, said Cambridge Police Sgt. Paul J. Sugrue.

"This will make it tough on me," said Suzie M. Miller '99, a member of the womens' basketball team who regularly bicycles between Currier House and Briggs Cage. "The streets in Cambridge are so crazy that riding on them is like putting your life in the driver's hands."

The ordinance is designed to cut down on collisions between bikers and pedestrians, Sugrue said, adding that several senior citizens have complained of problems in recent months.

Cambridge police will especially concentrate efforts in the Harvard Square business district, though the ordinance also bans cycling along the river houses and in the area bounded by Garden Street, Appian Way, Brattle Street and Mass. Ave., according to Surgue.

Harvard University Police Lt. William K. Donaldson, however, said it is not his officers' responsibility to enforce the city ordinance.

"It's up to Cambridge," he said. "But we want to get the word out to let returning sophomores and juniors know. We'll repeat the message in the fall with presentations to the first-year class."

Miller, one of many students who regularly bicycle through the Square, said forcing cyclists onto the streets will add several minutes onto their daily commute and place them in harm's way.

"There's not enough space on the sides of the roads," she said. "There's a bike lane part of the way [to the Quad], but not all of it."

Cambridge City Councillor Anthony D. Galluccio said the city plans to add bicycle lanes to Harvard Square over the next several years. Lanes already grace much of Mass. Ave. and nearly all of Mt. Auburn Street, he said.

"We do get calls from elderly residents who are intimidated," Galluccio said. "But we realize it's dangerous to bike in the Square, and we want to promote non-motor vehicle transportation. We're trying to find some middle ground."

The ordinance will reinforce the current law that bicycles sport front, rear and side reflectors. Also, cyclists must continue to obey all other traffic laws