Flag Drops to One-Third Mast : Track and field: Mike Marsh is the only U.S. runner to make the semifinals of the 100.

The opening day of competition in track and field’s fifth World Championships was so distressing for U.S. sprinters that it invited comparisons to that afternoon during the 1972 Summer Olympics at Munich, Germany, when Eddie Hart and Rey Robinson arrived too late for their 100-meter heats.

Never before or since had the United States failed to send at least two sprinters to the 100-meter final of a major international meet . . . until Saturday, when only one managed to advance as far as the semifinals .

The three Americans at least showed up at the starting line, although the most decorated of them in the 100 meters, 1994 No. 1 Dennis Mitchell, did not get much farther down the track before pulling up in the first round because of a strained left quadriceps muscle.

Maurice Greene, the Kansas junior college student who was impressive early in the season but not since, reached the second round before meekly bowing out, sixth in his heat in 10.35 seconds.

Left holding the flag for this afternoon’s semifinal and--he hopes--tonight’s final, is Mike Marsh, who ran the day’s best time, a wind-aided 10.03, in the second round before a Ullevi Stadium crowd of 38,521.

If the former UCLA sprinter did not quite establish himself as tonight’s favorite, it was because of the impressive performance of a current Bruin, Ato Boldon, who set a Trinidad & Tobago national record with a legal 10.04 in the second round. Only three men have run faster this year.

“The pressure is on the big dogs--Linford Christie, Donovan Bailey, Mike Marsh, Frankie Fredericks,” said Jon Drummond, a member of the U.S. sprint relay team who trains with Boldon under Coach John Smith at Westwood. “Ato is the kind of guy who steps in and foils their plans. I won’t be surprised if he wins. In fact, I’m expecting it.”

Boldon, 21, has no such expectations. After winning California junior college championships in the 100 and 200 for San Jose City College, he won the 1995 NCAA 200 in his first year at UCLA. But, although he ran in the 1992 Summer Olympics and 1993 World Championships, failing to advance beyond the quarterfinals in either, this is the first time he has really competed at this level.

“I just hope to show I belong here,” he said Saturday.

Such modesty is neither expected of nor heard from Great Britain’s Christie. Even though he, at 35, recently became a grandfather, he is also the reigning Olympic and world champion. More experienced than anyone else in the field in international competition, he barely exerted himself in advancing to the semifinal in 10.15.

Marsh, who turned 28 Friday, is best known as a 200-meter runner after winning the Olympic gold medal at that distance in 1992, but he said after winning the U.S. championship six weeks ago in the shorter sprint that he believes he is equally capable of becoming the world’s best in the 100.

He made it clear Saturday, however, that he does not expect Christie to merely hand over his title.

“I’ll run as fast as I can, then look at the scoreboard and see how I came out,” Marsh said. “Linford doesn’t enter into the equation until afterward, when they pass out the medals.”

Neither should discount Bailey, who, in trying to erase the stigma attached to Canadian sprinters since the Ben Johnson steroid scandal, has run the world’s fastest time this year--9.91--and qualified for the semifinals here in 10.18; or Namibia’s Fredericks, the 200-meter world champion who, like Marsh, is trying to establish himself in the 100. Finishing second to Marsh in the second round, Fredericks ran a windy 10.09.

Mitchell can usually be found in the company of the favorites after winning bronze medals in the 1992 Olympics and ’91 and ’93 World Championships, but he feared this year might be different after suffering a cramp in his quadriceps while working out last week.

“When you’re running that fast, it’s a fine line whether you’ll blow up,” he said. “I didn’t blow up. But the wick was lit.”

It’s too early to tell whether Saturday was the beginning of a bad era or just a bad day for U.S. sprinters. Among those who did not qualify for the 100 here, Carl Lewis might be too old at 34, world-record holder Leroy Burrell has been injured for more than a year and Drummond and Andre Cason are inconsistent.

U.S. track officials hope that Greene, 20, leads a new wave. He has the chutzpah for it, proclaiming himself ready for prime time after beating Lewis last spring. But he discovered here that he was not in the Kansas Relays any more.