Early in last night's rock concert at the Capital Centre, police began quietly escorting selected members of the audience out of the arena, one by one.

Within 3 1/2 hours, as the rock group Aerosmith played on and most of the audience listened, happy and unaware, a strike force of more than 70 police officers had made 25 arrests, most of them on drug-related charges.

The surprise crackdown by Prince George's County police followed a pattern set by similar operations that started in 1978 with the aim of damaging the Largo arena's reputation as a kind of safety zone for the drug subculture.

The number of arrests last night, made by a force that included undercover officers planted around the arena, was bigger than that in either the 1978 crackdown, in which 19 persons were seized, or last year's reprise, in which 12 were taken into custody.

"Ninety percent of what we're looking for is the things we see going on," said Capt. Richard A. Shaner of the county police.

"Any kind of violation we see going on," he continued, "if the situation is right and we can make an arrest, we make the arrest."

Both money and drugs were confiscated from the persons taken into custody last night, Shaner said. Drugs included "stuff burned in the Centre," he said, ". . . marijuana . . . PCP . . . and some pills."

Shaner said police know there is drug use at the Centre. But he said last night's crackdown did not stem from any particular upsurge in recent weeks or months.

"This is just a response to everything in general," he said.

In a similar crackdown at the Capital Centre last March, police made arrests after several undercover officers allegedly bought drugs from those taken into custody.

Shaner said he was reluctant to give details of procedures used by police in last night's crackdown, fearing that the aims of the operation could be compromised.

"The purpose of the thing is to try to discourage what's going on out there," he said.

As the concert approached its close last night, county police, aided by Maryland-National Capital Park and Planning Commission police, continued arresting suspects in the crowd of about 18,000.

Arrests were expected to continue, Shaner said, until police were overwhelmed by the required paperwork. Suspects were being taken to the Bowie police station for processing. All were described as men, 18 or older.

The 1978 crackdown, five years after the Centre opened, was described as a depature from a general hands-off policy toward drug abuse at the arena. Previously, police had cited the possibility of disorder as one reason for looking the other way. There were no reports of incidents connected to last night's arrests.