The four American men stepping onto the podium to receive gold medals after the men's 4x100-meter medley relay Saturday night did so with far fewer burdens than they started the day with. They collected their olive wreaths and medals and still felt as if they weighed less.

Winning the race was not much of an issue. They faced a weak field, with the Australians nowhere to be found, and won by nearly three seconds in a world record 3 minutes 30.68 seconds. But the Americans' barriers had been more mental than physical. It took the last race of the Olympic swimming competition to lift them.

''I had a feeling we were going to do something special,'' the breaststroker Brendan Hansen said.

Aaron Peirsol, who swam the leadoff leg, had won two gold medals, but the second one came after a harrowing debate over whether an illegal turn should disqualify him. He used this relay to break the world record in the 100-meter backstroke at 53.45 seconds.

Hansen, the world-record holder in both breaststroke events, failed to win a gold in either race here and found himself uncomfortable with his teammates' public insistence that the swimmer who beat him used an illegal kick.

Ian Crocker was swimming the butterfly leg only after Michael Phelps gave up his final swim so Crocker would have a chance to win his only gold medal.

Crocker had swum a disastrous leg of the 4x100 freestyle relay, failed to get out of the preliminaries in the 100 free and lost to Phelps in the 100 butterfly. After Phelps's gift, however, Crocker swam the second-fastest butterfly relay leg in history.

Phelps, who watched from poolside waving an American flag and leading cheers, met Crocker after the medal ceremony with a hug.

''He said, 'Congratulations,' and I said, 'Thank you,''' Crocker said. ''He gave me a great opportunity, and I wanted to take advantage of it.''

Finally, Jason Lezak brought them home on the freestyle leg, helping to erase a painful meet in which he was caught from behind in the 4x100 freestyle relay, finished 21st in the 100 free despite being ranked No. 1 in the world and finished fifth in the 50 free.

''Everything just kind of fell into place tonight,'' Peirsol said. ''It was just a great way to end our meet.''

The victory lifted the United States men's team to its ninth gold medal and its 18th over all. The relay also allowed Phelps to earn his sixth gold medal because he swam on the team in the preliminaries.

The women's team managed 11 medals -- only 3 gold -- and in their final race, they claimed a disheartening silver medal behind Australia in the medley relay.

Jenny Thompson did, at age 31, collect her 12th medal over four Olympics by swimming in that relay. It was her second silver medal of the Games, both in relays, and she is now the most decorated United States Olympian in history.

''I wanted to do a little better here, but I'm proud to be here at all,'' Thompson said. ''It's not the medals that are important to me. It's my love for the sport. Now that this is coming to a close, I can step back and see what the medals mean. They represent a lot of hard work and a lot of fun.''

Thompson started the butterfly leg of this relay with a significant lead because of an Olympic-record swim by Natalie Coughlin in the backstroke leg and a very good breaststroke leg by Amanda Beard. But Thompson was overtaken by Petria Thomas of Australia, who beat her by more than two seconds.

The American freestyler Kara Lynn Joyce could not catch Jodie Henry in the final leg, and Australia finished with a world record of 3:57.32.

Thompson had started the night by finishing seventh in the 50 freestyle, a race won by the defending Olympic champion, Inge de Bruijn of the Netherlands, in 24.58 seconds. That was followed by a surprisingly close race in the men's 1,500 freestyle, in which Grant Hackett of Australia took a big early lead but needed a last-lap kick to hold off the American Larsen Jensen.

It was Hackett's second straight Olympic title at that distance, the only one he swims without facing the towering presence of his countryman Ian Thorpe.