Dissident Soviet poet Nizametin Akhmetov, who is being held in a mental hospital, has learned that he will no longer be allowed to emigrate, the PEN American Center said in New York. An administrator for the literary group, Jane Yeoman, said Akhmetov, 40, smuggled a letter out of the Chelyabinsk Regional Hospital in the Soviet Union addressed to Yelena Bonner in Moscow, saying officials had demanded that he sign a pledge that he did not want to emigrate to the West. He asked Bonner, wife of human rights activist Andrei D. Sakharov, to "help as you can." The poet wrote that he was being administered drug treatments and was losing his ability to think. Last month, a Soviet official told former West German Chancellor Willy Brandt that Akhmetov would be allowed to emigrate.