LONDON (AP) _ The New Statesman, a left-wing weekly, has reported what it says are details of a secret British agreement with Chile for help in the 1982 Falkland Islands war with Argentina.

The magazine, quoting unnamed British government sources, said in its issue Wednesday that Britain was allowed to use an air base in southern Chile for Royal Air Force surveillance planes disguised with Chilean markings.

As part of the deal, the magazine said, Britain destroyed aircraft at Argentine air bases and used Chile as a base for infiltrating troops for espionage in Argentina.

Britain and Chile exchanged intelligence, with Chilean naval intelligence personnel breaking Argentine codes, the weekly said.In return, Britain gave Chile surplus aircraft and dropped restrictions on arms sales to Chile, the New Statesman said.

It said Britain also hindered U.N. investigations into Chilean human rights abuses by opposing the appointment of U.N. special investigators.

Britain recaptured the Falklands during the 10-week war after Argentina invaded the islands, which it has long claimed.

A Defense Ministry spokesman, who in accordance with British practice refused to be identified, said Britain withdrew its ban on arms sales to Chile in 1980.

An agreement for Britain to sell surplus planes to Chile was reached before the Falklands war, although some of the planes were not delivered until after the conflict, he said.

On the magazine's other military allegations, the spokesman said: ''We do not discuss the operational deployment matters and, therefore, cannot comment on suggestions that Chile made facilities available during the conflict.''