What started out to be a decisive test of skill this weekend between Britain's two great world-class runners, Steve Ovett and Sebastian Coe, has been transformed by unfortunate circumstance into something different, which should be a memorable race nonetheless.

A stress fracture has forced Coe to withdraw from the 3,000-meter contest Saturday night in London's Crystal Palace. But organizers have succeeded in gathering many of the world's other top middle-distance runners and sportswriters here now are predicting the best race in Britain since the 1948 Olympics.

Among the competitors are record holders in the mile, 1,500 meters, 3,000 meters and 5,000 meters from the United States, Britain, Kenya, New Zealand and West Germany. The field will include three of the four currently best 3,000-meter specialists.

The Americans include Steve Scott, who set the U.S. record for the mile at 3.47:69 in Oslo last week. He holds the world's third-best time at 3,000 meters. The others are Sydney Maree, a South African who attends Villanova University and is applying for U.S. citizenship, and Doug Padilla, who paced marathon star Alberto Salazar in a recent 5,000-meter race and is expected to be the pacesetter for a record finish in this contest.

The British participants feature Ovett, a world record holder and Olympic champion whose rivalry with Coe has enlivened British track for years. Ovett was injured last winter and had knee surgery. He has been coming back gradually, hoping to be at top form for his meetings with Coe.

They were to include an 800-meter race in Nice next month and a mile race in Eugene, Ore., in September. Coe's injury raises doubts about the other races, keeping alive at least for now the mystery of which of the two actually is the fastest. A previous golden mile scheduled for Crystal Palace in 1980 was scrubbed because of an injury to Coe.

Last Friday, Ovett dropped out of a 1,500-meter race in Paris and was taken to a hospital, where he was found to be suffering from colic, dehydration and exhaustion, probably a result of too quick a return from his injury. But doctors have approved his racing Saturday and he says his stomach is feeling fine.

The other British entry is a new star, David Moorcroft, who broke the world 5,000-meter record in Oslo last week, coming in at 13 minutes 00.42 seconds. Of Moorcroft's performance, Coe said: "It was a super, stupendous run, one of the greatest athletic performances of all time."

Kenya is sending Henry Rono, who holds the 3,000-meter world record of 7 minutes 32.1 seconds, set in 1978. Also on hand will be a talented newcomer from Kenya, Peter Koech. Kenya's athletic federation considered banning Rono from the British race because of his refusal to join an African team in the United States recently, but that threat has been removed.