WILMINGTON, Del. — Michael S. Berg and his son Nick could not have been more different.

Nick Berg, who was pro-Bush and a supporter of the Iraq war, was, in his father's words, a "marine wannabe" and a devoutly religious Jew. Michael Berg has been a pacifist and an atheist most of his life.

But Michael Berg says he and Nick shared a belief in taking a principled stand. It is this belief that Mr. Berg says inspired his Green Party bid for Delaware's only Congressional seat in the wake of Nick's kidnapping and killing in Iraq two years ago.

"Nick stood by what he thought was right," said Mr. Berg, a 61-year-old former teacher who is trying to unseat a seven-term Republican, Michael N. Castle. "I plan on doing the same."

The videotaped beheading of Nick Berg, a 26-year-old freelance radio-tower repairman, shocked a world audience after it was broadcast on the Internet.

And while Mr. Berg admits that he faces an uphill battle to topple a popular incumbent, he faces an even tougher personal struggle to find political purpose in the anguish over his son's death.

"I'm in this race to win," said Mr. Berg, wearing his standard outfit — jeans and an antiwar T-shirt — while seated in the cafe in downtown Wilmington that he uses for interviews, since his wife forbids members of the news media in their home. "But the larger point is to get more people talking about the war."

In a state where only 621 of 545,000 registered voters are signed up with the Green Party, Mr. Berg said he had raised a little over $5,000 of the $250,000 that his campaign director says he needs to be competitive.

As he bicycles across the state giving speeches at schools and churches and holding fund-raising house parties, he says he has found a receptive audience, not just to his call for an immediate withdrawal of all American forces from Iraq but also to the rest of his platform: universal health care, a livable wage and increased spending on education.

"A lot of voters are frustrated by the lack of options beyond the two major parties," Mr. Berg said. "And a lot of these people have not been voting before."

Elizabeth Wenk, a spokeswoman for Mr. Castle, said, "All I can say is that we welcome him into the race."

Mr. Castle, a moderate Republican who supports the war, is a former two-term governor and is the longest-serving congressman in Delaware history.

Mr. Berg said that he was originally approached by a representative of the state's Democratic Party to oppose Mr. Castle but that he opted to go with the Greens because "the Democrats have the money to get the message out, but they have the wrong message."

Dennis Spivack, 58, a Wilmington lawyer and a Vietnam veteran who is pursuing the Democratic nomination for the Congressional seat, said he could not imagine the trauma that Mr. Berg's family had experienced. But he added that he advocated a more responsible plan for withdrawal of American troops.

"We don't want to pull out in a way that will make things worse in that region, especially at a time when Iraq is on the verge of a civil war," Mr. Spivack said.

Mr. Berg said that in deference to his family's desire for privacy he initially avoided speaking in public about his son's death. But he soon changed his mind, drawing attention after telling reporters that his son "died for the sins of George Bush and Donald Rumsfeld."

He has not stopped talking about the war since.

"It is pretty discouraging that there are so many families in the same awful position," he said, adding that since his son's death he has become a close friend of Cindy Sheehan, who lost a son in the war and has become a highly visible war protester.

Mr. Berg concedes that his campaign has put strains on his family. His daughter, Sara, 33, a lawyer in Virginia, has sought answers about her brother's death by filing freedom of information requests with various branches of the government.

"Most of what she has received is useless," Mr. Berg said.

Mr. Berg also has a son, David, 35, who works in the print industry in New Jersey.

Mr. Berg moved from West Chester, Pa., 10 months ago because, he said, the news media were putting too much of a burden on his wife, Suzanne. When the Wilmington newspaper printed a profile article on Mr. Berg, his wife canceled their subscription because she did not want to risk seeing again the now-famous photograph of Nick kneeling in front of his masked executioners.

"This is not an easy balancing act," Mr. Berg said of his life as a political candidate.

When he returns home, he makes sure to put away his antiwar and campaign materials so his wife does not see that photo, which is on a poster he carries with him while campaigning.

"The truth is, when I'm not at work, I don't want to see it either," he said.