By Daniel Wallis

(Reuters) - NASCAR champion Tony Stewart said on Friday that killing a fellow driver this month will affect him for the rest of his life, but that returning to racing this weekend would help him to deal with the tragedy.

Stewart has missed three races since he struck and killed 20-year-old Kevin Ward Jr. in an Aug. 9 accident during a non-NASCAR sprint race in upstate New York. He will take to the track again this weekend in Atlanta.

An emotional Stewart said on Friday it was one of the toughest tragedies he has ever had to deal with, and "something that will definitely affect my life forever."

He told a news conference in Atlanta it was a sadness and pain which he hoped no one would have to experience, and that he could not possibly imagine the grief Ward's family was feeling.

The three-time champion said he wanted them to know he was thinking about them and praying for them every day.

"I've taken the last couple of weeks off out of respect for Kevin and his family, and also to cope with the accident in my own way," Stewart said. "It has given me the time to think about life, and how easy it is to take it for granted.'

But he missed his team and teammates, he said. "I think that being back in the car this weekend with my racing family will help me get through this difficult time," he said.

The results of an investigation into the crash are pending, but authorities said early in the probe that they had found no evidence of criminal behavior by Stewart.

The two drivers bumped cars during the race and the collision sent Ward into an outside retaining wall. During the ensuing caution period, Ward jumped out of his car in an apparent attempt to confront the 43-year-old Stewart, who remained in the race.

When Stewart came around on the next lap, his car appeared to fishtail, striking Ward and throwing him some 50 feet.

Stewart said on Friday he knew people wanted answers, but that he had to respect the investigation and stay quiet for now.

"Emotionally, I'm not sure if I could answer them anyway," he added.

(Reporting by Daniel Wallis; editing by Gunna Dickson)