The father of a young Soviet economist allegedly held in a psychiatric hospital for his critical writing appealed to international medical organizations today for help in obtaining his son's freedom.

In an open letter given to foreign correspondents here, Vasily Tyurichev, a Communist Party member, said his son, Valery, has been held for two years in a special psychiatric hospital in Smolensk after writing a critical analysis of the Soviet economy.

Valery Tyurichev, 27, was declared a schizophrenic for writing his manuscript, the father said. "Help a man who se sole guilt is that he is a man, in other words that he thinks," the father wrote in a typewritten appeal addressed to the World Psychiatric Association, the World Health Organization and Communists throughout the world.

The distribution of the appeal coincided with the first public mention here that the Soviet Union had quit the World Psychiatric Association last month, shortly before the organization was to consider western charges that the Soviets were abusing professional standards by their use of psychiatry to stifle political dissent.

An article in the English-language weekly, Moscow News, commenting on the withdrawal, asserted that the western allegations were false.

At its next congress in Vienna, the World Psychiatric Association was to have discussed American and British resolutions to suspend or expel the Soviet organization because of the alleged abuses.

Vasily Tyurichev said his son was fired from his job after sending his manuscript about the Soviet economy to the Communist Party Central Committee in 1980. Valery Tyurichev subsequently asked permission to emigrate and was arrested and committed to a special psychiatric institution in his home town of Dnepropetrovsk in March 1981.

The appeal said that Valery, a graduate of Dnepropetrovsk Trade Institute, was diagnosed as a paranoid schizophrenic and moved to the institution in Smolensk, where he was treated with insulin and haloperidol. According to his father's letter, the son was asked during psychiatric tests why he wanted to emigrate and he replied that "he could not trust the government in a country in which the kind of treatment he was receiving was possible."

Vasily Tyurichev said in the letter that his son had started a hunger strike Feb. 16 and that his life was "hanging by a thread."

Soviet dissidents repeatedly have accused the authorities of using psychiatric hospitals for dealing with particularly difficult political offenders. The authorites have repeatedly and categorically denied these charges.

Human rights activists who formed a committee to investigate the charges were arrested here in late 1979 and 1980 and given long prison terms on charges of anti-Soviet agitation.

The Soviet decision to resign from the World Psychiatric Association came a few months after the Union of Psychiatrists and Neuropathologists, as the Soviet psychiatric organization is called, offered to arrange for a foreign panel of experts to visit Soviet hospitals and investigate charges that psychiatry was being used against political dissenters. The offer was made last December.