As the finish line neared and his competitors fell back, Michael Johnson, without turning his head, peered left, searching for the track clock. About to win his fourth straight world title in the 400 meters, Johnson wanted to see if he also had reached the one milestone he had chased, unsuccessfully, for nearly 10 years.

The clock, Johnson's only competition tonight, told the 32-year-old Olympic and world champion that he had finally broken Butch Reynolds's 11-year-old world record. Johnson's time of 43.18 seconds topped Reynolds's 1988 mark by .11 seconds. He so dominated this race at the world track and field championships that silver medalist Sanderlei Claro Parrela of Brazil trailed by about 10 meters, a ridiculously large margin in a race so short.

"Coming off the curve, I knew I had a big lead," Johnson said. "I had to just keep telling myself, `Don't panic.' "

When Johnson realized what he had done, he raised his right index finger and let out a yell. But once he had come to a halt, there was no leaping or wild celebrating. Johnson simply looked satisfied. He posed for photographers by the clock, which flashed "NEW W.R.: 43.18." Spotting an American flag in the stands, he walked over to that section and happily slapped hands with about 60 fans with front row seats at Olympic Stadium.

In erasing what Johnson had this week called a "glaring" hole in his resume, Johnson showed an awesome sense of purpose and determination. He now owns world records in both the 400 and 200 (19.32 seconds), a mark he set during the 1996 Olympics. In winning his eighth world championship gold, Johnson also tied Carl Lewis tonight for the career lead in that category.

When he finally made his way around the stadium for his victory lap, carrying a small American flag, Johnson took his time. Unlike Morocco's Hicham El Guerrouj, who celebrated his 1,500 victory Tuesday by sprinting with his nation's flag, Johnson walked. This, he figured, was a moment he wanted to savor after a year in which he has battled nagging hamstring problems.

"I'm proud of myself for being able to come back," Johnson said. "I didn't tell a lot of people, but my coach [Clyde Hart] and I sat down at the beginning of the year, and he said: `What do you want to do this year?'

"I said, `Break the world record in the 400.' "

Said Hart, Johnson's coach since his college years at Baylor: "When Michael sets a goal, he's pretty hard-headed."

The 400 record has been particularly difficult to achieve. Before Reynolds set the world mark in 1988, Lee Evans had held the record for nearly 20 years. Evans ran a 43.86 at the 1968 Olympics in Mexico City.

Johnson looked as if he could have broken the record during Tuesday's semifinal heat in which he coasted -- amazingly -- to a time of 43.95. He said he worked during his three qualifying heats to perfect his first 100 meters, taking care not to go too fast out of the blocks, a common mistake among those 400 runners who also compete at 200 meters. His goal for the first 100 meters was running it in 10.9 seconds. With that accomplished, he said, he tried to relax over the next 200 meters.

As he rounded the final turn, he was a picture of intensity, pushing forward as his competitors seemed to be running in place.

"Coming home, I just tried to hold my form together," he said.

The hot night didn't bother him; after all, he had trained in Texas this summer as he recovered from a slight right hamstring injury. "It's 107 in Dallas," he said. "So this is okay for me."

Johnson acknowledged that his chase for this record had become exceedingly difficult since the U.S. track and field championships in June. When he pulled out of the 200 meters there because of a hamstring injury, he was accused of trying to duck a matchup against star sprinter Maurice Greene.

"It just wasn't fun leading up to this," Johnson said. "I always said, `When it's not fun, I don't want to do this anymore.' There were serious doubts for me for a while: Do I want to do this if it's not fun anymore?"

Tonight, Johnson said, he had a blast.

And he's ready to move on to the next challenge.

"I know," he said, "I can run 42 seconds."

Notes: Marion Jones, who could not complete her 200 quarterfinal Wednesday because of back spasms and cramps, officially withdrew from the rest of the world championships. USA Track and Field reported that she is "in good spirits but still experiencing back pain and spasms" and continues to undergo treatment. U.S. women's coach Lance Harter said he had not decided who would replace Jones in the 4x100 relay on Sunday. . . .

Australian Cathy Freeman won her second straight women's 400 title, narrowly defeating Germany's Anja Rucker. . . . Reston's Rich Kenah easily won his 800 first-round heat in 1:47.95. . . .

American Gail Devers, running in just her fifth hurdling event in the last three years, posted the fastest qualifying time tonight in the 100 hurdles quarterfinal (12.53). Not far behind was Sweden's Ludmila Engquist, who finished third overall with a 12.65. Engquist is striving to defend her world title despite undergoing chemotherapy treatment this summer for breast cancer.