A British military helicopter crash-landed in Chile today in mysterious circumstances leading to speculation that its crew had been carrying out a military mission near a nearby Argentine base.

A Defense Ministry announcement here merely said the Sea King helicopter "got into difficulties in appalling weather conditions and was lost, presumably while attempting to reach Punta Arenas, Chile to make an emergency landing."

British reporters who visited the site of the landing in Chile said, however, that they saw no bodies or blood. The reporters and Chilean officials surmised that the three-man crew had landed and, thinking they were in Argentina, destroyed the helicopter and gone into hiding.

The reporters for BBC-TV and Independent Television News said the Chilean authorities later destroyed their film and declared the landing site off-limits. They also burned up the remains of the aircraft.

Chile lodged a formal protest to Britain over the violation of its territory. The Sea King has a combat range of 240 to 330 nautical miles, but it was lost 450 miles from the Falklands, near which the British task force is centered.

The location has led to speculation that the helicopter either flew from a ship close to the Argentine coast or possibly was operating from an airstrip at Punta Arenas, 120 miles from the main Argentine southern airbase at Rio Gallegos.

If the crash of the helicopter pointed to Chilean cooperation with Britain, it could be embarrassing for the Santiago government--which has its own border dispute with Argentina.

Earlier this week the Argentine media reported that seven British commandos had been captured near the Rio Gallegos base.

The Sea King was the sixth helicopter reported lost by the task force during the Falklands operations. None is known to have been downed by enemy fire.