Stéphane Dion attacked the prime minister over the government's agenda on same-sex marriage, women's programs and judicial appointments, in his first appearance in the House of Commons since becoming Liberal leader.

Moments before question period, Dion received a standing ovation from all party members and Prime Minister Stephen Harper and the other party leaders crossed the floor to shake his hand.

But then Dion questioned Harper, saying "why on Earth" is he closing 12 of the 16 status of women offices across Canada "if it is not to cripple those who dare challenge his government's neo-conservative ideology."

Harper first responded by congratulating Dion for his "well-earned" victory and wishing him a "very long time" living in the Opposition leader's official residence.

But then he shot back that the money was being reallocated to programs from bureaucracy, and added a reference to the sponsorship scandal.

"When this government reallocates money, it does so to make it more effective for ordinary people, not to flow it into party coffers," he said.

Dion also pressed Harper about the coming vote on same-sex marriage, asking why he wants to be the "first prime minister in Canadian history to override the Charter?"

Harper instead zeroed in on whether Dion would force all of his MPs to vote against reconsidering same-sex marriage.

"I hope that proves not to be the case because I think the rights of members of Parliament are some of the most important rights we have in this country," Harper said.

Dion also challenged Harper over proposed changes to the process of appointing judges. The prime minister defended the changes, saying they will let crime victims and police have a say.

Conservatives have given notice that they're going to hold Dion accountable for previous Liberal shortcomings.

Dion, a former environment minister, ran for the party leadership on a green platform. His backers even used green scarves, T-shirts and caps as identity badges.

Yet under the Liberals, greenhouse gas emissions rose 30 per cent.

"He was part of the Liberal team during the entire Liberal debacle on the environment," John Baird, president of the Treasury Board, told CBC News on Monday. "He can't escape the collective responsibility."

The Conservatives are pleased that the Liberals finally have a leader because the Opposition will now have to make its policies clear, Baird said.

Dion has "no concrete plan" to deal with climate change, and now "he's going to have to talk about facts," said Baird.

70-page plan

Dion has a 70-page plan for the environment, and is expected to make the issue one of the key planks whenever a federal election is called.

He said that as a party, the Liberals represent social conscience, a strong market economy, and "the most important thing that everything else depends on — the environment."

Dion was elected in a tight race on Saturday, and has identified the Liberals as the party that cares. "Do we want an additional useless tax cut or do we want to put 800,000 kids out of poverty in this country?" asked Dion.

MPs watching Dion

Conservative and Bloc Québécois opponents said they'll watch Dion closely.

"I want to see what he does first. But one thing I'm sure is I don't want to underestimate his capacity," said BQ MP Vivian Barbot.

Liberal MPs are also watching. Some from Quebec have openly questioned whether Dion, a strong federalist, can win seats in their province, which turned to the BQ and Conservatives after the sponsorship scandal.

Dion authored the Clarity Act, which established tough ground rules for any future vote on the separation of Quebec.

Conservative strategist Goldie Hyder said the Tories won't underestimate Dion, calling the new Liberal leader an anti-establishment choice, like Harper.

But Dion's "old Liberal approach" of governing through a strong central government is at odds with that of the Conservatives and many Canadians, he said.

"Mr. Dion believes the government plays the better role in its relationships with the provinces, that the government knows better than the people," said Hyder.

"Mr. Harper … trusts the people and empowers the people and provinces."

John Wright, a pollster with Ipsos-Reid, said Dion has a laundry list of tasks ahead of him.

"He's trying to answer the media's questions, he has to heal the party, he's got a lot of emissaries he's got to send out," said Wright. "He's got a job to do in the House of Commons."

"We'll have to see whether the Liberal army comes back to fight the Conservative army."

Liked as environment minister

Environmentalists liked Dion when he was the minister, lauding him in 2005 when he chaired a UN meeting on global warming. But the Climate Action Network, a group of international environmental organizations, said under Tory Environment Minister Rona Ambrose, Canada went "from hero to zero."

However, Conservative Baird made reference to the recent report from environment commissioner Johanne Gélinas, saying it made Liberal shortcomings clear. 

Gélinas said Ottawa needs "a believable, clear and realistic plan to significantly reduce greenhouse gas emissions," with short- and long-term national goals.

The Conservatives have introduced a plan to cut greenhouse-gas emissions in half by 2050.