Amnesty International has charged that torture of political detainees in Turkey is ''widespread and systematic'' with ''no effective action by the authorities to stop it.''

In a report issued Tuesday, the London-based human rights organization detailed its ''major concern'' with treatment of Turkish prisoners since the military coup of 1980 and said the number of complaints diminished ''only relatively after the return to constitutional rule in 1982.

''The reports have come from a wide range of sources and have included numberous first-hand testimonies by former prisoners, supported in a number of cases, by medical examinations,'' the report declared. It included interviews with numerous alleged victims but did not specify in how many cases Amnesty felt the evidence of torture was conclusive.

Amnesty investigates reports of torture and mobilizes members to adopt the cause of specific political prisoners and to write to authorities in an attempt to obtain releases.

The report said Amnesty ''has submitted the names of more than 100 people alleged to have died in custody since September 1980.'' It said Turkey accounted for 82 names, including deahts attributed to suicide, accident or illness, and nine persons listed as still alive.

Turkish Ambassador Sukru Elekdag, in a statement circulated by a Gray & Co. pulbicist, said allegations in the report'' are either inaccurate or false.'' He said his government investiaged all torture charges and ''jpersons accused of mistreatment have been indicted, tried and those found guilty approximately 105 in the past five years given stiff jail sentences. Damages have been awarded to victims and to their families.''

Amnesty aimed its criticism at Turkish police.