A British charter airliner with 138 passengers and eight crew aboard crashed today in mountainous terrain as it approached for a landing and there appeared to be no survivors, airport sources reported.

The wreckage of the Dan Air Boeing 727 was spotted at about 6,000 feet in an isolated area and sources said that it would take rescuers some time to reach it.

The plane was due to land at Los Rodeos Airport, scene of the world's worst air disaster in March 1977 when two Boeing 747s of Pan American World Airways and the Royal Dutch Airline KLM collided on the runway, claiming 583 lives.

Dan Air, Britain's largest charter operator with more than 60 planes, said most of the passengers, who included three children, were vacationers from Manchester, England. The Canary Islands are a favorite vacationing spot for Britons. It was not known whether there were any Americans aboard. s

In London, a spokesman for the airline said the plane was more than three hours overdue when it crashed at about 8:25 a.m.

Airport sources said the plane lost contact with the Tenerife control tower five minutes before it was scheduled to land.

United Press International quoted an air traffic controller at the Tenerife airport as saying the last radio message received from the plane was "a call for help."

The controller said the pilot asked for permission to land but gave no indication of trouble before the communication with Los Rodeos broke off.

The weather at the time of the crash was described as variable with clouds at 1,000 feet. United Press International also reported that confusion arose when the tower at Las Palmas Airport on neighboring Grand Canary Island tried to reach the plane on an emergency frequency.

Other towers, hearing the message, thought it came from the missing jetliner until they played back their recordings.

Spanish rescue services at first thought the aircraft had plunged into the Atlantic Ocean and ships and helicopters scoured the waters north of the island about 200 miles off the coast of Morocco.

But later, two people telephoned police to report they had heard an explosion in a mountainous area about 16 miles south of Los Rodeos Airport. Shortly afterwards, airport sources said the wreckage had been spotted.

An unconfirmed report said the control tower at the new Reina Sofia airport south of Santa Cruz also received a distress call from the airliner.

The worst air disaster in U.S. aviation history occurred last May 25th when an American Airlines DC10 jetliner lost its left engine and crashed shortly after takeoff from Chicago's O'Hare International Airport, killing all 272 persons aboard and three persons on the ground.

Tenerife is a 795-square-mile Spanish island, the largest in the Canary chain, located in the Atlantic Ocean off northwest Africa.