The Liberals and New Democrats brokered an "agreement in principle" to secure NDP support for the government on the budget vote, and against any efforts by the Tories and the Bloc Quebecois to bring it down.

"This agreement is fiscally responsible and it is progressive," said Prime Minister Paul Martin said late Tuesday at a news conference in Ottawa.

But the deal comes with a hefty price tag. 

Martin had to agree to guarantee $4.6-billion in new investment over the next two years. 

The money will come out of a projected surplus (before contingencies) of approximately $9-billion, and will go toward the environment, affordable housing, foreign aid, training, and post-secondary education

A good chunk of the money -- $1.6-billion -- will go to new affordable housing programs. Another $1.5-billion will be given to the provinces for reductions in post-secondary tuition fees and for training programs for the unemployed.

After the parties' house leaders negotiated all day over the compromise in the budget that could fend off a snap election, Martin said his party also reached an agreement with the NDP to put off tax cuts for large corporations -- but keep them for small and medium-sized businesses.

At least $4-billion will go to debt-repayment, said the prime minister.

"Under no circumstances will we go back into deficit," stressed Martin. "The fiscal integrity of this country . . . remains a fundamental element of our ability to finance social programs and our ability to create jobs."

"Why are we doing it? We're doing it to make Parliament work," said Martin.

Earlier, NDP Leader Jack Layton announced that he's agreed to a deal with the government that will see more money put into environmental and social programs through the budget.

"This budget isn't perfect, but it's better and it's balanced," he said.

Under the tentative agreement, Layton said: "Families will pay less for kids' education, workers will get better training. We'll reduce pollution, build affordable housing, protect pensions, and have a better place in the world Canadians can be proud of."

The deal also includes:

• $900-million for environmental programs and public transit;
• $500-million for an increase in foreign aid; and
• $100-million for a workers' pension protection fund.

CTV chief parliamentary correspondent Craig Oliver said with this deal, the Liberals are hoping to have "increased the price Stephen Harper will have to pay for killing this House of Commons."

But most of all, Oliver said the Liberals are hoping to change the ballot question: "That is, that Canadians will vote not on the basis of Gomery revelations; but on real, bread-and-butter social benefits they will say Canadians will lose if they vote Conservative."

Reacting to the agreement, Conservative Party Leader Stephen Harper told CTV News that the new spending won't make Canadians forget about the sponsorship scandal that's hammering the minority Liberals.

"Four-point-six billion dollars is a lot of taxpayers' money for Mr. Martin and for Mr. Layton to pay to make corruption go away," Harper said.

Will NDP support be enough?

The Prime Minister will likely need the support of the 19 NDP seats in the House of Commons if he hopes to get his budget passed.

Failure to do pass the budget would amount to a vote of non-confidence, and could push the minority Liberal government into an election.

CTV Ottawa bureau chief Bob Fife said although the government comes away from the announcement looking like it cares about social issues, the tentative agreement "still doesn't leave the Liberals in that great a situation. They still don't have the numbers to get the budget passed."

The Globe and Mail reported Tuesday that the Liberals may have lost the support of at least one Independent, Chuck Cadman.

Lawrence Martin, a columnist for The Globe, told CTV's Canada AM that Cadman had originally sounded like he would vote to prop up the government. But his constituents want him to vote to bring the government down.

"Mr. Cadman, a key figure in this fight, said yesterday he would vote to defeat the Liberals," Martin said.

"So that decreases the chances, even if this package is accepted by Mr. Layton, that the Liberals can hold off the election until the fall or the winter."

The combined Bloc Quebecois-Conservative alliance would amount to 153 votes, with 151 for a Liberal-NDP combo. That leaves three Independents.

Independent Carolyn Parrish has said she will vote for the Liberals because she doesn't think Canadians want to go to the polls. Ex-Liberal David Kilgour has not clearly stated how he would vote.

Meanwhile, a poll conducted after Martin's televised speech last week suggests that the event did not help boost his Liberals.

The Decima Research poll, conducted Thursday to Sunday, put Conservative support at 32 per cent, compared to 27 per cent for Liberals. The NDP received 21 per cent support, and the Bloc Quebecois came in at 58 per cent in Quebec.

The Decima survey of just over 1,000 Canadians is considered accurate to within 3.1 percentage points, 19 times out of 20.

With a report from CTV News and files from The Canadian Press