It became clear today why British athletes were so desperate to compete in these controversial Olympics. They grabbed one of the top prizes in track and field today and figure to get two more Saturday.

Sprinter Allan Wells became the traditionally accepted world's fastest human by boring into a gusty wind and sticking his chest just far enough out at the finish to edge Cuba's Silvio Leonard in the 100-meter dash.

Daley Thompson took a commanding lead at the midpoint of the decathlon competition and Steve Ovett and Sebastian Coe ran well enough in their 800-meter semifinal heats to gain a matchup Saturday track devotees have been keenly anticipating for months.

That 800 final has taken on the dimensions of a fight, partly because neither runner has any affection for the other. But the major punch today was delivered by a gifted heavyweight, Teofilo Stevenson.

There were whispers that, at 29, Stevenson was no longer quick enough or fit enough to win the gold medal in his third straight Olympics; that, in fact, he is the second-best heavyweight in his own country. That all may be true, but stevenson still is armed with what made him exceptional -- a lethal right.

It landed on the jaw of Nigerian Solomon Ataga today in the final eight seconds of the first round -- and there was no second round.

Ataga had dropped his left hand a bit after failing to land a jab and Stevenson almost wound up before planting another infamous right. Ataga was wobblylegged nearly a minute afer being hit, and the goodhearted Stevenson was one of those who helped him to his corner.

It was the first of four victories Stevenson needs to win the gold, and he said during a brief interview conducted while he strode toward a bus back to the Olympic Village: "I'm in the best shape ever to win the gold."

Coe and Ovett also are confident before their confrontation. They are the world's best middle-distance runners at the moment and finally meet here Saturday after avoiding each other for a long time. And the possibility of someone else taking advantage of their attention to each other and sneaking off with the gold medal also lessened.

That happened when Olaf Beyer not only failed to win his heat, as expected, but finished fourth and failed to qualify for the finals.

In separate heats, Coe and Ovett won coasting. Coe said: "It was a bit windy out there, but the joke of it is that these are the conditions I'm used to, more so perhaps than some of the other runners.

"It looks good for the final. I feel very relaxed."

In the 100 final, Wells and Leonard were as far from each other as is possible on the track and as close to each other at the end. Both were timed in 10.25 seconds. In Lane one, Leonard did not appear confident of victory a few steps past the finish line, even though photographers judged him the apparent winner and recorded his every more.

From lane eight and after a poor start, Wells also was uncertain, until he saw a videotape replay near the track. Certain his lead had earned the gold, Wells threw his hands into the air and, as photographers readjusted their attention, pranced a lap around the track in celebration.

His reception was unusually quiet. It had nothing to do with Wells. What had happened was that his victory coincided with the final, memorable performance of one of the finest athletes in the history of the Soviet Union. p

Just before the sprinters took their marks, Viktor Saneyev triple-jumped for the last time in an Olympics -- and nearly leaped into the record books. Had be jumped just 4 1/2 inches farther, the 34-year old Saneyev would have been only the second athlete to win gold medals in four straight Olympics.

Still his 56 feet 6 3/4-inch effort moved him from third place to the silver medal, past world record-holder Joao de Oliveria of Brazil. And Saneyev's reception was far greater than the one given the Soviet winner, Jaak Uugmae.

The unfortunate Wells was on his victory lap while the crowd still was devoting full attention to Saneyev. Pehaps if it had heard the interview Wells gave to British television a few minutes later, the reaction might have been nasty.

"Being in Russia, it's not easy to do things," he said."And his (Leonard) being Cuban put it all against me. It was very close. The start was not particularly good, but good enough."

Leonard seemed to relax ever so slightly the final 20 meters. That might well have cost him the chance to become the second Cuban of the night to mount the victory stand.

The first was an emotional Maria Colon, who won the women's javelin with a throw of 224 feet 4 inches that bettered by nearly eight feet the Olympic record set in qualifying Thursday by Ute Richter of East Germany. o

After five decathlon events, Thompson was 264 points ahead of his nearest rival, Yuri Kutsenko of the U.S.S.R., and also well ahead of the first-day paces he and West Germany's Guido Kratschmer had set during world-record performances earlier in the year.

In topping Thompson's record last month and setting the 8,649-point standard, Kratschmer, who is not competing here because of the West German team's boycott, had 4,460 points his first day.

The 22-year-old Thompson had the best performances of the day in three of the five events, the 100 meter dash (10.26), long jump (26 feet 3 inches and 400 meters (48.01).

Had he endured the qualifications successfully and matched that time in the open 100, Thompson would have won the bronze medal. The third-place finisher, Peter Petrov of Bulgaria, could muster only 10.39.

Well's victory surely will be challenged by boycotting American sprinters, among them Stanley Floyd. When he won the event at the U.S. trials, the freshman at Auburn said: "I want to meet whoever wins the Olympics. Then we'll decide who ought to get that gold medal."

Because Britain decided to protest the Soviet invasion of Afghanistan by not permitting its flag or anthem to be used during medal ceremonies, Wells watched the International Olympic Committee's flag raised and a Soviet band play the Olympic hymn without much inspiration.

Because he was facing the opposite direction, Wells did not see his countrymen hoist three British flags in the stands, one enormous and the others quite a bit smaller.

Several familiar athletic names failed to qualify for finals in their specialties: John Akii-Bua, gold medalist in '72, finished seventh in a semifinal heat of the 400-meter hurdles and Italy's Pietro Mennea, East Germany's Eugen Ray and James Gilkes of Guyana missed the sprint final.

Also, Bulgaria's Totka Petrova, reinstated in a controversial ruling voiding a ban for life for steroid use, finished sixth in a heat of the women's 800 meters and failed to advance. Three Soviets qualified for the finals.