Crowds of youths, some of them boisterous, swarmed for the second straight night in and around the Merriweather Post Pavilion in Columbia, scene of a rock music performance.

Although no arrests were reported last night, Howard county police said many of the young throng appeared to be under the influence of drugs and at least three young men were taken to a hospital for treatment of apparent drug effects.

The crowd attracted by a rock group known as The Who, was estimated at 20,000 to 25,000, at least 40 per cent more than the maximum capacity of the outdoor amphitheater.

Gates Thrown Open

Gates to the pavilion were thrown open to admit the large, unpaid throng gathered in the area.

Police said this was done by the pavilion management in an effort to avoid injuries which might have resulted from a repeat of the Sunday night incident in which about 100 youths described as "hippie-types" stormed the gates in an effort to gain free admission.

As hundreds of gate-crashers took over pavilion seats last night, police said, more than 100 irate ticket holders returned to the box office to demand refunds for seats they were unable to claim.

A spokesman for the pavilion management said today that the gates were opened to non-ticket holders about 40 minutes after the start of the 8 P.M. performance because that "was the best way to avoid trouble, to avoid a stampede of any kind."

A performance by a musical group called Pen Lucy preceded the main concert by The Who, a guitar-smashing British quartet.

Efforts were made to admit