Today, Boston becomes the launching point on the road to Beijing.

Deena Drossin Kastor, the 2004 Olympic bronze medalist in the marathon from Agoura Hills, makes an attempt to qualify for her third Olympic Games today at the U.S. Olympic Women's Marathon Trial in Boston.

Kastor heads a field of 162 entrants — including four other former Olympic marathoners and five other Olympians — racing for a top-three finish to earn a spot in the field in Beijing this August. The race begins at 5 a.m. PDT, with live coverage streaming on NBCSports.com. A one-hour highlight show will air on MSNBC on April 27.

"I am really excited for the trials and to make my third Olympic team," Kastor wrote in an e-mail last week. "I have gotten in pretty good shape to fulfill my goal of making the team and winning the trials. I will never take for granted that other women are also well prepared, so it will take a large effort to win."

Kastor, who qualified for the 2000 Olympics in the 10,000 and placed second in the 2004 U.S. trials before earning her bronze medal in Athens, last ran the marathon distance in Boston last April, finishing fifth on a rainy, windy morning.

"I was really fit and ready to run well," she recalled in a recent conversation. "I just for some reason fell short with the weather, and not feeling that great the morning of the race. And it's unfortunate that it has to play out like that, but I guess that's the tossup of the marathon sometimes. Because my preparations went great until then."

She has, however, continued to compete at other distances while training for the marathon, most recently winning the U.S. 15k championship in Jacksonville, Fla., in early March, while keeping an eye on both the trials and the larger goal.

"I want to be really fit for the trials so I can recover very quickly, be really fit so I can make the top three," she said, "but also to recover quickly enough to be able to be ready for the Olympic games as well, because it's going to be a quick turnover."

Today's race precedes the fabled Boston Marathon by a day, but is not run on the same course. In keeping with recent trials, it is run on a criterion course, a closed course which begins and ends at the traditional Boston Marathon finish line and includes a 2.2-mile "city loop" which includes a number of the Boston's tourist attractions, and a flat six-mile "core loop" the athletes will run four times.

"It's a wonderful course," said Kastor, who scouted it last year when the national 10k championships were held in Boston.

"You go around Boston Common, which is really hilly, in the beginning, but after that, you stay on a flatter loop. And just from being in New York for the men's trials (last fall), it was awesome to see how the criterion course works, that it really did spawn a lot of interaction between the crowd and the athletes.

"There were so many people in the center of the circle running from one part of the park to the next to be able to see the runners as frequently as possible. So I see it working in Boston as well, to be able to leap around and see the paces shifting and places shifting. It makes it more exciting for the racers and the spectators alike."

Kastor's second-place finish at the 2004 trials was on a hilly criterion course in St. Louis.

"This one is much flatter," she said. "The biggest challenge, I think, for the course in Boston is we go over the Charles River twice on each loop, so if it's a cold, blustery day, you could definitely be affected by the wind from the river."

A preliminary forecast appears fairly favorable, with temperatures from the mid-40s to mid-50s during the race period, with no precipitation and light winds.

For Kastor and the other runners, a lengthy period of aiming for the Olympics comes down to a single day. Certainly, this is not without risk, as demonstrated in November, when Meb Keflezighi — the silver medalist in the men's marathon in 2004 — finished eighth, ending his hopes of competing in Beijing.

Not all countries hold a qualifying race, but Kastor has no problem with USA Track and Field's method of determining the Olympic team.

"I think our system is very fair," she said. "A lot of countries have selection processes, and that seems a little unfair sometimes, that people end up getting left out when you feel they clearly belong on the team. I think it's just more political when they choose someone.

"But to be ready on that day is what the Olympic Games are about, also, so the people that can rise to that pressure and be ready on that day. In saying that, in St. Louis (in 2004) I was second and didn't win the trials, and Jen Ryan was very close behind. So I may not have made the team if the course was about 300 or 400 meters longer.

"So it can be a very harsh reality in making or not making the team, but I do really believe that our system is the fairest of them."