Amnesty International appealed to Soviet President Leonid Brezhnev today for "the unconditional release of all prisoners of conscience and for an end to the abuse of psychiatry for political purposes."

The London-based human rights organization, which won the Nobel Prize in 1977 for its work on behalf of political prisoners, said in an open letter to Brezhnev that the appeal was the start of a major campaign against Soviet human rights violations.

The campaign is being timed to coincide with preparations for the 1980 Oympics in Moscow. Amnesty's letter said the organization would use the Olympics "as an opportunity to inform international opinion and the many thousands of visitors to the Olympic Games about the reality of Soviet political imprisonment."

Amnesty accused the Soviet Union of ordering the transfer of political and religious prisoners from jails and psychiatric hospitals in the Moscow area to distant parts of the country "to prevent any potential contact between these prisoners and the thousands of foreign visitors to Moscow during the Olympic Games."

The organization said it believes the detention of some dissidents has been prolonged to keep them in custody during the Olympics. It said that a Ukrainian physician, Mykola Plakhotnyuk, who was to have had his case reviewed for possible release from a psychiatric hospital, was told: "Until the Olympic Games have been held, there can be no rush in your case."

Amnesty condemned the confinement of at least 100 more Soviet dissidents in psychiatric hospitals since a 1975 Amnesty report on the issue.

"Virtually anyone from any national, religious or social group who publicly criticizes your government's practices," Amnesty said in the letter to Brezhnev, "is in danger of being certified as mentally ill."

Amnesty also charged that since the Soviet government signed the Helsinki human rights agreement in 1975, it has imprisoned 19 Soviet citizens who tried to monitor violations of the accord. "Amnesty International does not know of a single case in which a Soviet court has acquitted a political or religious defendant" charged with crimes like "hooliganism," "parasitism or "anti-Soviet agitation and propaganda" after making an accusation that human rights had been violated, it said.

Amnesty also cited cases of Soviet citizens being imprisoned for trying to organize independent trade unions, for seeking greater artictic freedom, and for advocating regional nationalism in Lithuania, Latvia, Estonia, Georgia and the Ukraine.