Chinese authorities are hunting bombers who killed two people in attacks on commuter buses yesterday morning, just three weeks before the Beijing Olympic Games begin.

The first bomb exploded at 7:05 a.m. on a bus at a stop on People’s Road West, one of the main thoroughfares of Kunming, the capital of Yunnan province, which borders Vietnam, Burma, and Tibet in China’s far south.

One person was killed and another 10 injured, according to local press. Web sites showed photographs of the bus with a gaping hole in its side and glass all over the road. The victim was named locally as Wang Dezhi, 30, who was with her husband going home to rejoin their daughter in an outlying area of the province and celebrate her birthday. The husband was also injured.

The second explosion happened on another bus on the same road about an hour later. Chen Shifei, 26, from the town of Lijiang, also in Yunnan, was killed and a further four injured.

BUSH GIVES ATHLETES OLYMPIC SEND-OFF

President Bush gave American Olympians a rousing White House send-off to next month’s games in Beijing, urging them yesterday to “compete swifter, higher, and stronger” but also be mindful they will be “ambassadors of liberty” to the people of China and elsewhere.

Mr. Bush is attending the opening ceremonies and the first few days of the August 8-24 games. Standing in the Rose Garden with about two dozen athletes who will compete in the Beijing Olympics and the corresponding Paralympics there in September, Mr. Bush said he is “fired up” to watch some of the competition.

“I can’t wait to salute our athletes, and I can’t wait to share in the joy of your triumphs,” he said.

WILLIAMS TO PLAY WITH INJURED LEFT KNEE

Serena Williams plans to keep playing through a left knee injury despite advice from a doctor and her father that she rest with less than three weeks before the Beijing Olympics.

She figures her injured knee “will be old news” by the time the Olympic tennis competition begins August 10.

Williams withdrew from Saturday’s semifinals of the Bank of the West Classic at Stanford after injuring her knee. She said that an MRI exam afterward showed an inflamed joint.

“I’ve been playing a lot of tennis, that’s basically what it is, a lot of use,” she said yesterday. “I haven’t had enough time to train the way I normally do off-court because I’m playing a lot.”

Ms. Williams, ranked fifth in the world and seeded second for this week’s East West Bank Classic, received a first-round bye, and is scheduled to play her opening match tomorrow against Czech Petra Kvitova.

“I’m taking it day-by-day and I’ll see how I go,” she said. “I’m doing rehab for it three times a day, just to make sure that I’m ready.”

Serena’s older sister, Venus, and Lindsay Davenport already withdrew from Carson because of right knee injuries, making for a rash of knee injuries on the American Olympic team.

FIRST WORKDAY OF NEW BEIJING TRAFFIC LAWS

Traffic flowed a little smoother. Busy avenues had fewer cars. By nightfall, even the hazy sky had mostly cleared.

So went the first workday under a government-imposed plan to reduce Beijing’s foul air pollution before the start of next month’s Olympics.

Millions of commuters turned to subways, buses, and car pools as the strict program sought to take half of Beijing’s 3.3 million cars off the road.

In parts of the city, traffic was visibly lighter than on other workdays.

“There were much fewer vehicles on the airport expressway, and I could drive much faster,” said civil servant Lin Kai, shaving with an electric razor while sitting in his parked car.

He said he bought a new bicycle because of the restrictions and would try to pedal to work a few times a week despite the summer heat and the hour-long ride.

The two-month operation that began yesterday bans cars with odd-numbered license plates one day, even-numbered plates the next. The ambitious attempt to ensure “blue sky days” by the time 10,500 athletes and 500,000 visitors arrive for the Olympics includes construction cutbacks and factory closures.

OLYMPIANS RECEIVING MASKS TO BLOCK POLLUTION

The U.S. Olympic Committee is distributing high-tech masks to more than 600 athletes because of concerns about pollution at next month’s Beijing Games, the Wall Street Journal reported.

The masks were developed in secrecy over a two-year period, though some American athletes haven’t decided whether to risk insulting their Chinese hosts by wearing them, the newspaper said.

Beijing officials instituted a $17 billion program to clear smog and have closed factories, halted construction, and restricted vehicle use in the city in an attempt to make the air safe for the Aug. 8-24 Games.