BOSTON Deena Drossin Kastor stood in the sheltering circle of a score of family and friends in the lobby of the Fairmont Copley Hotel on Monday, clutching a bouquet of spring flowers and gamely smiling as well-wishers patted her on the back and whispered kind words in her ear.

The baseball cap she had worn to shield her face from the wind and rain on the Boston Marathon course was still pulled low across her forehead as she tried to make peace with an unhappy race.

"It was a tough day out there," she said.

Kastor expected a laurel wreath, not a bunch of tulips. But somewhere in Wellesley, the Agoura High graduate had to stop at a restroom, and the race slipped past her.

Kastor finished fifth in 2 hours, 35 minutes, 9 seconds, behind winner Lidiya Grigoryeva (2:29:18) of Russia, Jelena Prokopcuka of Latvia, Madai Perez of Mexico, and Rita Jeptoo of Kenya.

As the first American woman, she won the U.S. national championship, but she was aiming for so much more. Instead of the blanket that is wrapped around runners at the finish line, Kastor had disappointment draped across her shoulders.

Holder of both the American record and the world-best time for 2006 (2:19:36 in the London Marathon), Kastor, 34, was coming home to her birthplace as the top-ranked marathoner in the world. She packed the months before Boston with fast finishes, winning the US Cross-Country Championships in February and the Gate River Run 15K in March, her 20th national title.

Kastor slogged through the rain with a slow lead pack of seven, sometimes eight, runners, for about half the race, but just as a trio of runners began to break away from the pack, an attack of cramps sent Kastor to the restroom near the 14-mile mark.

"It's hard to say what would have happened if I hadn't stopped," she said, "but I had to stop."

Kastor lost more than a minute of race time and any chance at victory. In 2007, the marathon stops for no one.

When she got back on the course, Kastor said she was in eighth or ninth place. She was encouraged that she was able to pick off a few runners as she got back into her rhythm, but she never got close to the leading threesome.

"It's hard to deal with a disappointing performance when you've prepared for something so much greater than what you did out there," Kastor said.

Kastor said she would come back, and not just because the 2008 Boston Marathon will serve as the Olympic Trials.

"It was my first Boston experience, and I will say it was everything I hoped," she said, but then her voice caught, just for a second. She pressed her lips together and went on, saying how much Boston meant. "This was my only focus this year," she said.

Kastor kept referring to the pace as pedestrian, as if they were walking in from Hopkinton. With no male runners to run behind because of the staggered start, Prokopcuka and defending champion Jeptoo reluctantly did most of the work leading the group.

"No one didn't want to help me, so I had to make pace and run alone," said Prokopcuka. "I don't like to jog, and when I was behind girls, it was simply jogging."

Kastor had a different view of the tactics.

"That toying around of the pace is never the way I like to run," said Kastor. "My strength is making a steady tempo run. I didn't want to take the lead and block the wind for everyone. I really felt I played it smart the first half of the race, with the intentions of running aggressively in the second half."

She never got the chance.

This was Kastor's second consecutive difficult marathon. She was sixth at the 2006 New York Marathon (2:27:54), when she sat back for too long.

This time, the difficulties were out of her control. But Kastor, a two-time Olympian (bronze medalist in 2004) who is hoping for a third shot at gold, said she is done with marathons for a while.

"I probably won't run a marathon in the fall," Kastor said. "I think I'm going to give my legs a rest and save my marathons for 2008."

Robert Cheruiyot won the men's race for the third time, defending his title in the remnants of a soaking nor'easter to bring Kenya its 15th victory in 17 years. He outkicked countryman James Kwambai on the way into Kenmore Square to win in 2:14:13 slower than the course record of 2:07:14 he set last year but enough to win by 20 seconds.