President Bush is promising the most tightfisted budget (search) of his presidency, one that would slash or kill 150 programs and freeze many others below the rate of inflation (search). Those ideas could run into a cold dose of budget reality.

Regardless of the party in charge, Congress keeps a constitutional grip on the nation's purse strings. And lawmakers seldom display much zeal for ending programs, presidential pleading or not.

The annual presentation of the president's budget is one of the top events on the nation's political calendar. But despite the hoopla that will surround the rollout of Bush's 2006 budget on Monday, the document for the budget year that begins Oct. 1 remains a presidential wish list, not a piece of legislation. A blueprint, a starting point.

"It obviously helps this president that both chambers are controlled by his party, so you're not going to get the knee-jerk partisan 'dead on arrival' kind of thing," said Stanley Collender, a veteran budget analyst at Financial Dynamics, a consulting firm. "But because the president is proposing big changes, it's going to be tough for him to get through a lot of what he wants."

After the president submits his budget — a massive multivolume document containing tens of thousands of entries — lawmakers spend the next nine months doing the heavy lifting and political fine-tuning. Actual decisions on spending and taxes are made through separate appropriations and revenue bills.

The process has been compared to making sausage, not something you want to watch.

"The people in Congress on both sides of the aisle have said, ;Let's worry about the deficit.' I said, 'OK, we'll worry about it again.' My last budget worried about it, this budget will really worry about it," Bush said Friday in Omaha, Neb.

However, Bush's own first-term track record is one of initiating costly new programs — three big tax cuts, a No Child Left Behind education act, a Medicare (search) prescription drug benefit — more than for getting Congress to join him in exercising restraint.

Examples:

—Last year, he proposed chopping Medicaid spending by $20 billion. Congress turned him down. Bush is likely to try again.

—He proposed eliminating 38 Education Department programs, including an exchange program for "historic whaling partners" that was championed by Senate Appropriations Committee Chairman Ted Stevens, R-Alaska. Nearly all are still in business, including the whaling one.

—Each time Bush has requested less for Amtrak than the railroad said it needed to survive, Congress raised the amount. This year, he's expected to propose ending operating subsidies for Amtrak entirely — something last tried, unsuccessfully, by President Reagan in the 1980s.

While preaching austerity, Bush is also proposing more money for some defense and homeland security programs and asking Congress to make his first-term tax cuts permanent. He says he's sticking to his goal of cutting the deficit — which the White House predicts will rise to $427 billion this year from $412 last year — in half by 2009.

Is that possible?

"It depends on what you mean by possible," said Alice Rivlin, former vice chairman of the Federal Reserve and budget director in the Clinton White House. "Can he put together a budget proposal that does that on paper? Yes. Can it pass the Congress? I doubt it."

"You'd have to be terminating large numbers of programs, turning things back to the states. It would be a drastic reversal of federal policy for which he has not prepared the country," Rivlin said.

And two major expenses won't even be in the 2006 budget: rising costs of military operations in Iraq and Afghanistan and a sweeping Social Security (search) overhaul that has already ignited bitter partisan fighting.

Some presidential budget initiatives are big deals when announced, but fade quickly. Remember Bush's mission to the moon and to Mars?

He put startup funds for the mission in his 2005 budget. Congress rolled it into funds for other space programs. Bush seldom talks about going to Mars any more, and didn't in Wednesday's State of the Union.

Bush also has drawn a blank on school vouchers to help parents defray private-school costs, a major 2000 campaign proposal. Congress ignored Bush's request last year for $50 million to encourage voucher programs in local communities.

The president has yet to use his veto pen, but that could change in his second term as he comes under increasing pressure to rein in deficit spending.

"The Republicans are deeply embarrassed by the exploding budget deficit and they are going to be looking to do something about it. The budget politics are going to be intense," said Thomas Mann, a political scientist at the Brookings Institution who closely follows the budget.