Prime Minister Jean Chretien's political career has spanned almost 40 years and on Thursday the House leaders of the various parliamentary parties offered their farewells as he prepares to retire.

The most emotional tribute came from Progressive Conservative House leader Joe Clark whose own political career extends back to the years when the Liberal party was headed by Pierre Trudeau.

"This prime minister earned his way to high office. Time and again he did the heavy lifting. Time and again he took hard decisions which Canadians in the end support," Clark said.

Like others, he cited Chretien's devotion to his constituents in his home riding of St. Maurice and the Canadian people.

"Never for a moment have I doubted his passionate commitment to Canada...it comes as the book says, straight from the heart. It is palpable, it is powerful, and it's part of what has made him seem so real and so genuine to ordinary people across the country," Clark said.

Clark, who once briefly served as prime minister himself, looked back at Chretien's years of service and into the days to come.

"I know that his successor, whatever his strengths may prove to be, will never strike that personal chord with the people of this country," Clark said in apparent reference to Paul Martin.

Alliance House leader John Reynolds called Chretien the "little guy from Shawinigan" and noted that seven prime ministers had served during his political career which began almost four decades ago.

"We have had sharp differences of opinion, however, at this moment in time we think it is appropriate to offer our best wishes and thanks on behalf of all Canadians to the prime minister. All political differences aside, he did his best and he did straight from the heart," Reynolds said.

NDP House Leader Bill Blaikie said that he has been in political office for 24 years of the prime minister's tenure. He called Chretien "a worthy and challenging opponent."

"I know that I speak for many Canadians when I say that he found his way to the right position when he decided that Canada would not participate in the war on Iraq," Blaikie said.

"We hope that this significant act of Canadian independence in an era otherwise marked by an increasing loss of sovereignty will be an inspiration to other Liberals."

The prime minister told the Commons there were times when he was forced to re-evaluate his own position on some issues and change "for the better."

"You know Mr. Speaker, when I arrived here in 1963, as the leader of the Bloc Quebecois (Gilles Duceppe) said, I had some different views -- indeed, I had some different views. But when I came into this House of Commons and I met the representatives from all parts of Canada, some of my views changed," Chretien said.

Clark was especially generous in his praise for Chretien's wife, Aline, who sat in the public gallery with son Hubert and longtime advisor Mitchell Sharp. The prime minister later thanked his wife for her support and she blew him a kiss from the gallery.

Earlier in the afternoon, Chretien introduced a bill that makes Canada the first country to take steps to offer low-cost drugs to poor nations struggling with such epidemics as AIDS and malaria. It could be one of his last acts in the House.

"Tributes here today are to a man -- but in a larger sense this is a Canadian, a Canadian success story about a democracy where ambition and ability and accomplishment can prevail," Clark said.

CTV analyst Craig Oliver said that even though some of Chretien's ministers went down amid conflict of interest allegations, history would likely regard him favourably.

"I think history will remember that Chretien left the country much more comfortable with itself, more prosperous, and certainly more secure in its unity than the country he took charge of 10 years ago," Oliver said.

The prime minister is expected to adjourn business in the Commons on Friday ahead of next week's parliamentary break. The House is expected to reconvene in late January or early February under Paul Martin's watch.

Globe and Mail columnist Jane Taber reports that Chretien is saving his big good-bye for the Liberal leadership convention in Toronto next week. Chretien's final Liberal caucus meeting turned into an emotional sendoff on Wednesday.

The caucus presented Chretien with his chair from the House of Commons, wrapped in a big, red bow. Chretien also received Tuesday's flag from the top of the Peace Tower and a scholarship of up to $500,000 was named in his honour.

Chretien played coy, refusing to confirm that the caucus meeting might be the last, adding -- as he has said before -- he'll step down sometime between now and the end of February.

"This has been my life," he said. "For me, the Liberal party is my family. The family will continue."

With a report from CTV's Craig Oliver