BEIJING — After months of speculation about how Olympic athletes would react to the air quality problems here, some answers arrived at the airport Tuesday, when four track cyclists on the United States Olympic team stepped off their flight wearing masks over their mouths and noses.

Yves Herman/Reuters

A cyclist from the U.S. team arrived wearing a mask at the Beijing airport on Tuesday ahead of the 2008 Beijing Olympic Games.

They were the first athletes at these Summer Games seen wearing masks publicly to combat the effects of pollution, and the sight of them drew considerable attention and criticism from United States Olympic officials.

The United States Olympic Committee had issued the specially designed masks to protect athletes from the potentially harmful air here. The U.S.O.C.’s lead exercise physiologist, Randy Wilber, had advised the athletes to wear the masks on the plane and as soon as they stepped foot here.

The track cycling events held indoors here begin Aug. 15, and some of the team’s members — Mike Friedman, Sarah Hammer, Bobby Lea and Jennie Reed — were prepared for the worst when they arrived in Beijing, knowing that the air quality was questionable.

Two of them wore their masks on the plane. The other two put on the masks when they arrived at the airport. Soon, photographs were splashed on television and on the Internet.

“This is really a surprise, because I didn’t think it was going to be such a big deal,” Friedman said. “Why we wore the masks is simple: pollution. When you train your whole life for something, dot all your i’s and cross all your t’s, why wouldn’t you be better safe than sorry?

“They have pollution in Los Angeles, and if the Olympics were in Los Angeles, we would probably wear these masks, too.”

But U.S.O.C. officials were apparently unhappy with that choice, scolding the cyclists for walking off the plane wearing the masks because it might embarrass the host country, Friedman and Lea said. The cyclists said they did not remember the name of the official who spoke with them.

“They told us that the Chinese were mad and that this is a politically charged issue, but we didn’t mean to offend anybody,” Friedman said. “When they handed us these masks, they never said, ‘Here they are, but don’t wear them.’ ”

Lea said, “It’s disappointing, because I was under the assumption that the mask was approved for use because it was issued by the U.S.O.C.”

Darryl Seibel, a spokesman for the U.S.O.C., said he was not aware of any reprimand. But he said the Olympians should feel free to wear their masks around the athletes’ village. Other United States teams, including the swimming squad, have been discussing when and where to use the masks.

“We’ve said all along that it is the athletes’ choice whether to wear one if they feel it’s necessary,” Seibel said. “I’m no scientific expert, but walking through an airport doesn’t seem like the place where it would be necessary to wear them.”

Earlier this year, Jacques Rogge, the president of the International Olympic Committee, said he was confident the air would be clean because Chinese officials “are not going to let down the world.”

Officials in Beijing, one of the world’s most polluted cities, promised the sky would be clean for the Olympics, but as the Games have drawn closer, officials were forced to take extraordinary measures. Factories in the city and in the surrounding provinces were shut down or moved. Major construction was halted. Half of the city’s cars were taken off the road.

But the sky remained thick gray this week, prompting some athletes to take precautions.

Months ago, Wilber, who did not respond to e-mail messages late Tuesday night, said he feared this would happen. He knew that wearing the masks ran the risk of offending the host country and creating political tension. In turn, he advocated that many teams train away from Beijing until just before their events.

Most of the track team, for example, is training in the coastal town of Dalian, about an hour and 15 minutes away by plane. But smog has unexpectedly coated that city, too.

The Chinese and the International Olympic Committee, including Arne Ljungqvist, the chairman of the I.O.C. medical commission, have repeatedly said that the air quality is not a risk to athletes.

During a previously scheduled news conference Tuesday night, Ljungqvist dismissed the track cyclists’ actions.

“I don’t see the need for it, honestly,” Ljungqvist said of the masks, although he noted that some athletes with respiratory conditions might need to wear them.

He said that officials were testing the air daily for the five major types of pollutants, and that conditions had improved since Olympians moved into their housing July 27.

“The mist in the air that we see in those places, including here, is not a feature of pollution primarily but a feature of evaporation and humidity,” Ljungqvist said. “I’m sure, I’m confident the air quality will not prove to pose major problems to the athletes and to the visitors in Beijing.”

The cyclists had been through this before in Beijing. At their Olympic test events last year, the smog even made its way into the velodrome, floating just below the rafters. Lea said he developed a “wicked sore throat” about 30 minutes after flying into Beijing. It turned into a chest infection that lasted a week.

Lea did not wear a mask then, but he saw others cyclists in them. He said he thought they “looked ridiculous.”

Erinn Smart, a fencer who has bad allergies, said she started coughing Monday because of the noxious air. Reluctant to be the first athlete to wear a mask, she said she wondered who would “start the trend.” She now has an intrepid group to follow.

“I think you’ll see more and more people wearing masks now,” Friedman said. “How do you control that? You just can’t.”