Ralph Maerz is a 56-year-old ex-smoker who until a month ago hadn't gone for a serious run since high school.

Yet on Sunday, he will be among the 30,000 runners in the New York City Marathon. He will be there because his son Noell cannot.

Noell Maerz, a 29-year-old father-to-be, was killed in the World Trade Center attack. A bond trader with Euro Brokers on the 84th floor of the south tower, he had been training for his first marathon.

Ralph Maerz was persuaded by another son, 27-year-old Erich, to join him in running for Noell.

They are among about 10 people who have signed up for the race to take the places of loved ones lost on Sept. 11.

"It's a way of doing something my son was going to do, and this way all three of us can compete together," said Maerz, of Lansdale, Pa. "The three of us — Erich and myself and my son Noell. Not in body, but in spirit, he will be there."

Organizers are dedicating Sunday's 26.2-mile race to the victims of the terrorist attacks and are collecting donations from runners and sponsors in hopes of raising $1 million. The race's new motto is "United We Run," and red, white and blue will be everywhere. Doves will be released at the starting line.

"This is going to be a major celebration of life for the city," said Allan Steinfeld, marathon director. "It's not just about the sport, it's all about New York."

Steinfeld said he expects a larger turnout than the usual 2 million spectators lining the route through the city's five boroughs.

Somewhere in that crowd will be about 15 friends and relatives of Ralph and Erich Maerz, cheering them on as they pass by wearing T-shirts with a photo of Noell and 8334, the number Noell was assigned for the race.

Stephen Comber will wear 18416, the number assigned to his nephew, Robert Peraza, who was a broker at Cantor Fitzgerald. Peraza, 30, had been training for his first marathon and sought advice from Comber, a more experienced runner.

Now Comber will compete instead.

"I almost feel like I'm not even doing it. This is Rob's race," Comber said. "As far as I'm concerned, he did the hard work, he trained and was ready to go. I'm just stepping in and running the last leg for him."

Comber had put together a training schedule for Peraza and had given him advice on everything from what to eat to what kind of sneakers to wear.

A few days after the terrorist attacks, Comber traveled from his home in Clifton, Va., to New York to comfort Peraza's parents. They went to Peraza's home, a few blocks from the marathon's finish line in Central Park.

"There were his running shoes, and above the bed was his training schedule with little checks on it, and it just sort of hit me," Comber said. "And I said, 'Man, we've got to finish this race."'

Unlike the Boston Marathon, the New York race has no qualification requirements. It is open to anyone over 18.

Noell Maerz was a backup quarterback at Hofstra University. He competed in triathlons and 10K races and was looking forward to his first marathon.

"I never even thought about running that far," his father said. "I told Noell he was crazy for running that thing."

Ralph quit his 35-year, two-packs-a-day smoking habit in 2000, hoping to get into shape someday so he could join Noell and Erich in a father-and-son experience: a minitriathlon of swimming, cycling and running. But at the time of Noell's death, he had not gotten around to starting his training.

As for running the marathon, "it's like the little red caboose, who said, 'I think I can, I think I can.' I hear Noell's voice, and I know I can," Maerz said.