Soviet police cracked down yesterday on a group of unofficial artists attempting to exhibit in Leningrad, some of the artists reported.

According to the artists, police blocked the entrance to the apartment where the show was to be held, prevented exhibitors from travling to Leningrad and sent home others who had already arrived.

Meanwhile, dissidents in Moscow said cdoctors handling the case of Vladimir Borisov have refused to release him from a Leningrad mental hospital as recommended by a medical commission.

In Belgrade, the wife of jailed dissident writer Mihajlo Mihajlov appealed to Yugoslavia's Vice President Vidoje Zardovic to transfer her ailing husband from prison to a hospital because a six-week hunger strike has left him in "dangerous condition."

A government spokesman denied that Mihajlov was in ill health.

In Warsaw, the dissident Workers Defense Committee released what it said was a secret government document indicating that authorities had anticipated workers' riots against food-price increases in June.

The document said the Interior Ministry and the manager of the country's biggest textile factory, at Lodz planned to broadcast a warning that any disturbances would be quelled by legal action. The announcement was canceled shortly before it was to have been broadcast, the document said.