Leningrad police arrested more than 150 persons last week at an impromptu outdoor rock concert, Soviet sources reported today, and now are seeking to blame the musicians for the July vandalism of priceless marble statutes in the city summer garden.

The arrests were made on August 28, the sources said, after city police unexpectedly broke up what had become a regular, informal summer jam session by members of several unauthorized rock bands. An eyewitness said the police brought dogs and truncheons into play, and held most of those arrested for more than 18 hours at district police stations for questioning.

KGB secret police are said to have questioned many persons, threatening them with 15 days in jail if they did not implicate the musicians in the vandalism case.

At least a dozen and perhaps as many as 30 statues that adorn Peter the Great's summer garden were damaged heavily, pulled down by vandals in mid-July. The treasures of Peter The Great's city are viewed by most Soviets as virtually sacred, and millions of rubles have been spent over the years to preserve and restore the czars' palaces after World War II destruction.

The vandalism has never been reported by the official national media, although a local Leningrad television station is said to have broadcast appeals for citizen assistance after the damage was discovered.

The musicians are said by informed sources to belong to various groups whose unauthorized works are known widely through tape cassettes. The bands are called "Rosianne," "Living," and "Aquarium" and have persisted despite repeated official attempts to break them up, the informants said.

These sources view the KGB efforts at linking the rock musicians to the vandalism as an attempt to finally disrupt the nucleus of the Leningrad's lively underground rock scene.