WASHINGTON (Reuters) - Top Republicans charged President Barack Obama with driving the United States toward socialism on Friday, opening an ideological attack on his big spending plans.

While the tough rhetoric was certain to rev up hard-line Republicans -- many of whom regard “socialism” as anathema to American life -- it was unclear how much it would change the debate in the Democratic-led Congress, which begins hearings next week on Obama’s $3.55 trillion budget proposal.

John Boehner, Republican leader in the House of Representatives, on Friday called Obama’s new budget proposal and recently passed economic stimulus plan “one big down payment on a new American socialist experiment.”

Obama’s budget proposal increases taxes on the wealthiest Americans to pay for more government attention to healthcare, education, climate change and social programs along with efforts to jolt the economy out of a deepening recession.

The budget also forecasts the biggest U.S. deficit ever at $1.75 trillion, adding to widespread sticker shock in Congress where Democrats already pushed through Obama’s $787 billion economic stimulus package with just three Republicans votes in the in the 100-seat Senate.

“The problem for Obama is more a question of whether the increased government intervention actually works -- gets the economy moving, creates the sense, within the next year-plus, that we are turning the corner,” said Norm Ornstein, a congressional scholar at the American Enterprise Institute.

“The second question is whether he can keep his own Democrats together behind his tax plan and his budget hopes,” Ornstein said.

MODERATE REPUBLICANS WORRY

The three Senate Republicans who crossed the political aisle to back the Obama stimulus plan have said they had reservations about his budget proposal.

“The president’s proposed budget outlines an aggressive domestic agenda that requires serious consideration, but also raises many questions, particularly about the enormous growth in the public debt,” said Senator Susan Collins, who along with fellow Republican Senators Olympia Snowe and Arlen Specter voted for the stimulus bill.

Democratic Senator Ben Nelson, who joined Collins in drafting a compromise on the stimulus package, also voiced concerns about the budget.

“While President Obama inherited much of the deficit he’s battling, his budget has eye-popping numbers, and its size and scope concern me. In particular, I’m not sure raising taxes is the best way to go in these times,” Nelson said.

Lawmakers are certain to make changes in the spending plan before it is brought up for passage in the House and the Senate, likely by early April.

Senator Judd Gregg (R-NH) (2nd L) and Representative Paul Ryan (R-WI) (C), ranking Republican members of the congressional budget committees, arrive for a news conference to discuss the proposed 2010 federal budget at the Capitol, February 26, 2009. REUTERS/Jonathan Ernst

Senate Republicans were able to force changes to the stimulus bill with procedural maneuvers. Budgets are not subject to such procedures, but Obama will likely need bipartisan support to win passage of the individual spending bills that implement the budget plan.

A group of 49 fiscally conservative House Democrats, whose commitment to deficit reduction has at times put some of them at odds with Obama’s economic program, hailed Obama’s budget for presenting what they called an honest fiscal picture.

“To begin to set our nation back on the right fiscal track, we must first understand and acknowledge how big of a hole we are in,” said Representative Stephanie Herseth Sandlin, a leader of the Democratic “Blue Dog” Coalition.

By invoking “socialism” -- a term many Americans equate with a frightening government takeover of the economy -- some Republicans appeared ready to use the budget debate to burnish their conservative appeal after last November’s election drubbing.

Senator Jim DeMint called Obama “the world’s best salesman of socialism,” while Senate Minority Leader Mitch McConnell said Obama’s proposals recalled the “big government mentality” of former Democratic President Jimmy Carter -- a favorite target for many in the conservative movement.

Ornstein said that while the Republican charges of socialism may play well in solidly Republican congressional districts as well as conservative radio and television talk shows, they might not get broader traction.

“I think that for most other Americans, it will either be ignored or will backfire,” he wrote in an email to Reuters.