Stephen Harper continues to refuse to apologize for accusing Prime Minister Paul Martin of being soft on child porn. The accusation, leveled in a press release last week, was later softened, but it's still reverberating on the campaign trail.

Harper has admitted that the headline from Friday news release -- "Paul Martin Supports Child Pornography?" -- was too strong, and that someone made an unfortunate mistake. But the Conservative leader has stopped short of apologizing.

"He has said he has zero tolerance. He does not have zero tolerance. He said it was his number one priority. It was not his number one priority," the Conservative leader said Saturday.

Martin, meanwhile, is looking for an apology. "His comments were clearly out of line and it is really beyond belief that he doesn't believe just how unacceptable they were," he told reporters in St. Jean-sur-Richelieu, Que.

The prime pinister said he has always felt "personally very strongly" about the issue of child pornography. He also said he didn't think there was a political party in this country that wouldn't "pull out all the stops" to ban such material.

Martin said the reason he voted against Conservative legislation on child pornography was because the Liberals had their own legislation and were focusing on that.

It's doubtful Harper will buy that argument. In the past, some groups have said Bill C-12, which would ban child pornography, would also infringe on artistic expression.

"These are excuses to let child pornography continue. It's an excuse to have weak laws on child porn," Harper said. "We're not going to pussyfoot around this."

The attack has brought a bizarre and ugly tone to the election campaign. But Martin is refusing to get involved in the mud-slinging. "I'm not in any position to judge," he said. Martin added that negative attacks were one of the reasons voters were cynical about politics.

"I'm not going to engage in that kind of thing. I think the political process should be much above that."

Martin said the upcoming election was an important one. "We're going to decide the way in which our rights are protected," he said.

Two other federal leaders didn't support Harper in his attack on Martin.

"When things like that happen, as a leader you should say 'I apologize' and say it was an error," said Bloc Quebecois Leader Gilles Duceppe.

"It shows a real failure in judgment on Mr. Harper's part and calls into question the kind of judgment he would exercise while in office," said NDP Leader Jack Layton.

Child pornography made its way into the news following a high-profile murder case in Toronto on Thursday.

Michael Briere, 36, pleaded guilty to first-degree murder in the 2003 death of 10-year-old Holly Jones. Briere admitted he had a long-term fantasy about sex with a young girl and had been looking at child pornography obtained over the Internet just moments before stumbled upon Jones.

Harper denied responsibility for politicizing the issue at a sensitive time. "It was Mr. Martin who chose to start this debate. He said it was his number one priority. He jumped on top of it and escalated it," Harper said. "This is being politicized because of Mr. Martin's incorrect remarks on this issue."

Oliver's analysis

Craig Oliver, CTV's Ottawa bureau chief, thinks Harper's child pornography stance will hurt his party.

"It's a bizarre and even vicious remark. No one -- even Mr. Harper, especially Mr. Harper -- believes, for God's sake, that Paul Martin is in favour and supports child pornography. I don't know what Mr. Harper's problem is with the word 'apology.'"

Legal scholars have pronounced Canada's child pornography laws among the toughest in the world, he said.

"And this is the problem for Mr. Harper, because first, it is slowing him down at a critical point in the campaign, when his campaign had gone flat and he's trying to get it going again.

"Second, it allows the Liberals to raise that old spectre again of right-wing extremism in the Conservative Party, which is the last thing they needed.

"And finally, Ralph Klein comes along -- who seems to have a case of national Conservative Party leader envy, because he's done this before to his own leaders -- and raises this whole issue of private medicine, which has put Harper in a bind on that one too," Oliver said.

While Oliver didn't think these developments were enough to tank Harper's campaign, he did say it was a nose-to-nose election.

"They don't need this. They have to get far past this and get back to their own agendas."