Hundreds of young people puffed away on what was said to be marijuana yesterday on Boston Common. Police stayed away most of the afternoon and no arrests were made.

A police spokesman insisted last night that no one was arrested because "no one was smoking marijuana." All indications however were that it was the real thing.

But smoking wasn't the only activity the crowd of over 1000 indulged in. Several members of a motorcycle club decided to put on a trick-riding show. First they zoomed around the Common, then they took off for adjoining Beacon St. with hundreds of young admirers trailing behind.

As the crowd blocked traffic, the cyclists whipped up Beacon Hill one by one, peeling out on their back wheels. Part of the crowd stood on the steps of the State House yelling, "Legalize Pot."

The crowd swelled and began to get out of hand. A group of about 20 surrounded a police car, rocked it, and nearly turned it over. An airport limousine got the same treatment. Finally about 40 people turned on a sightseeing carriage, terrifying many of the children and old people inside. No one was hurt.

After a half hour of these disturbances the police arrived and dispersed the crowd. But the men in blue conspicuously ignored the scores of people on the grass still smoking grass.

The affair was sponsored by a loosely-organized group known as the Committee for Sensible Marijuana Legislation.