PHILADELPHIA (AP) _ Bands of youths attending a lunchtime parade Monday to honor retiring basketball star Julius Erving broke windows, looted stores and slightly injured two police officers, authorities said.

Police arrested 21 juveniles and 16 adults on charges of vandalism. To head off damage, a downtown mall closed for three hours, according to authorities.

''Roving gangs caused all kinds of turmoil,'' said officer Tony LaSalle.

Officer Theresa Young said windows were broken all along the parade route.

The violence started while Erving, who is retiring after 11 years with the Philadelphia 76ers, was speaking at a rally after the parade, Ms. Young said.

One uniformed police officer was struck in the back of the head with a rock, and a plainclothes officer was thrown to the ground by someone trying to grab her purse, said Detective Gerald Whartenby.

Neither officer was injured seriously, he said.

The Gallery, a mall with 200 stores several blocks from the parade route, closed at 1:30 p.m., said Ricardo Dunston, vice president and general manager of Rouse Philadelphia Inc., which manages the complex. They later reopened.

Erving rode with his wife, Turquoise, in a 1928 Packard Roadster behind nine high school and college marching bands and a dozen other antique cars carrying current and former Philadelphia teammates.

Whartenby said 600,000 to 700,000 people watched the parade, many from office windows. Police estimated 15,000 to 20,000 congregated at a downtown plaza to hear Erving and public officials speak.

At JFK Plaza, Erving gave a 10-minute speech thanking his former teammates for their help in his 16-year career.

While Erving was speaking, police began receiving reports of youths breaking windows at downtown stores, Ms. Young said.

Some of the crowd headed toward Jewelers' Row, where police hastily put up barricades and asked jewelers to pull down protective metal grates.

Whartenby said one jeweler's window was broken.

''They broke my window and stole everything in the window,'' said Michael Carmes, owner of Aurum Jewelers. He said the jewels, mostly diamonds, were worth $7,000 to $8,000.