Englishmen Steve Ovett and Sebastian Coe, co-holders of the world record for the 1,500-meter run (3 minutes 32.1 seconds), tonight glided through their semifinal heats at that distance in fine form, providing a tantalizing overture to the most important footrace of the boycott-plagued Moscow Olympics.

The duel between Ovett and Coe, determined countrymen with vividly contrasting personalties and running styles, for undisputed world supremacy in the glamorous middle distances, would excite the imagination at any Olympics.

At the Moscow Games, which have been boycotted by the United States and approximately 50 other countries because of the Soviet invasion of Afghanistan, Friday's dream 1,500-meter final is regarded by some observers as a saving grace: a reminder that the Olympics are about sports as well as politics.

Ovett, 24, the silent and sometimes surly competitor who looks and runs like a bulldog, won his semifinal in a rather leisurely 3:43.1, characteristically waving his arm triumphantly before the finish. Tonight, in fact, he waved while he was still in second place, before accelerating out of the final turn and cruising home with a flourish.

Coe, 23, won his semifinal in 3:39.4. Having run Wednesday's first-round heat as a foot-runner, he decided to try another tactic and held back in fifth place until 200 meters were left.

Then he turned on the smooth speed that has earned him four world records (he holds three currently), fluidly overtaking everyone on the last turn, before easing up and crossing the finish line just ahead of East German Jurgen Straub.

Ovett, who stomped a sluggish and unresponsive Coe on Saturday in his own best event, the 800 meters, looked confident to the point of arrogance. That is his nature anyway, and he has not lost a 1,500 meters or a mile since May 1977, winning 28 races at 1,500.

Coe, who hasn't run a 1,500-meter race this year and has never faced Ovett at the distance, looked pleased with his form, too.

His semifinal was the last track and field event of the night at Lenin Central Stadium -- run as the Olympic torch burned brightly atop the massive arena against a purplish-black sky -- and at the end he was smiling broadly, pumping his fists like a prize-fighter who is ready for the biggest bout of his life.

Also qualifying for the final were Straub (3:33.7 last year), Jose Marajo of France (3:35.1), Vittorio Fontanella of Italy, Dragan Zdravkovic of Yugoslavia, Andreas Busse of East Germany, Steve Cram of Britain, Jozef Plachy of Czechoslovakia and Robert Nemeth of Austria. All of them, with the possible exceptions of Straub and Marajo, should wind up understudies to Ovett and Coe.

The 1,500-meter semifinals, overshadowed finals today in which Bronislaw Malinowski of Poland overtook tired and fading Filbert Bayi of Tanzania for the gold medal in the 3,000-meter steeplechase, Yuri Sedykh set a world record to lead a Soviet sweep in the hammer throw and Tatyana Kolpakova of the Soviet Union won the women's long jump.

On the political front, International Olympic Committee Director Monique Berlioux said that the group's executive board decided today to use the flag of the city of Los Angeles and the Olympic hymn in lieu of the Stars and Stripes and "The Star-Spangled Banner" in the closing exercises Sunday, indicating that the next Summer Games will be held in Lost Angeles in 1984.

In the steeple chase, Malinowski, 29, an exuberant Pole, let Bayi wear himself out with an overly ambitious pace and blew by him to win the gold medal in 8:09.7.

Bayi, as is his wont, immediately jumped into the lead and set a murderous pace. He strung out the 12-man field quickly and led by 35 yards with two laps of the 400-meter track to go, but then faded when his ambition exceeded his means.

The bearded Malinowksi, silver medalist in the event at the 1976 Montreal Olympics, started closing the gap quickly as they came up to the gun lap. He practically jumped on Bayi's back as they went over the second hurdle.

Malinowski, getting stronger as Bayi slowed with exhaustion, passed the front-runner on the next-to-last curve and was 10 yards in front by the time they reached the water-filled steeplechase barrier. He won with plenty to spare, raised his arms in a victory salute, blew kisses to the crowd with both hands, then trotted around the track in the opposite direction to avoid the prohibition here on laps of honor.

Ecstatic Poles in the crowd who had cheered a world record by pole vaulter Wadyslaw Kozakiewisc 24 hours earlier, again sang, danced, waved their red-and-white national flags and chanted "Pol-ska, Pol-ska, Pol-ska."

"The pace was too fast. The first 800 meters, it was an eight minute pace," said Malinowki, a teacher who speaks fluent English. "I was running 30 to 40 meters behind Filbert. That was my tactic. Many times I've run very fast for the first 1 1/2 kilometers, and too slow the second 1 1/2. This time I did it the other way."

"One kilometer before the finish, I knew that I would defeat Bayi, because he is running the last kilometer much slower than the first two. You cannot keep up such a pace."

Bayi, who held the world record for 1,500-meters and the mile in 1975 but missed the Montreal Games because of the Black American boycott, had raced in only one steeplechase since 1972, losing to Malinowski earlier this year in Stockholm.

Bayi resumed training in December 1979 after a troublesome calf injury and four bouts with malaria. He dropped out of the 1,500 meters here to concentrate on the steeplechase, but is not as fluent in the technique of the event, with four barricades and a water hazard, as Malinowski, who has been running it for 18 years.

"It is much different from a flat race. It is important to be good technically on the jumps," Malinowski said, "because over the distance you have 35 obstacles, and you spend 925 seconds on each of them, so that is about seven seconds altogether. Your techical skills have to be very good."

Having finished fourth in the 1972 Olympics at Munich, second in Montreal an first here, Malinowski says the goal left for him is the world record of 8:05.4 held by Henry Rono of Kenya, an absentee today because of the boycott. Malinoswki will seek the record at a meet in London on Aug. 8.

"It is difficult to go for a record in the Olympics," Malinowski said, "because your tactics are to run for the medal. I have been waiting 13 years for this medal. Now I can go for the record.

Bayi finished second in 8:12.5 and Eshetu Tura of Ethiopia was third in 8:13.6. "My pace was too fast.I really felt it in my shoulders and in my legs. They got tired," Bayi said. "But the silver is the first medal ever for Tanzania in the Olympics Games, so I am very happy."

Sedykh, the second gold medalist in track and field from the 1976 Games to win here (East German sprinter Barbel Wockel in the women's 200 meters was the first), broke his own world record by tossing the hammer 268 5 1/2 on his first throw.

That led a second consecutive Soviet sweep of the event as Sergei Litvinov took the silver medal with an opening throw of 267-7 (he fouled on his next five attempts) and Yuri Tamm captured the bronze at 259-1. "Those Soviet fellows may be good with a sickle," quipped an American spectator, "but they're even better with the hammer."

Kilpakova won the long jump with a leap of 23-2 on her final attempt. Brigitte Wujak of East Germany, jumping immediately after Kolpakova, fell short at 23 1 1/4 and Tatyana Skadhko of the Soviet Union -- who had the best three jumps going into the last of six rounds -- took the bronze at 23-0. This was the first time three women had exceeded 23 feet in an Olympic long jump competition.