The centerpiece provision of the sweeping corporate tax cuts steaming through Congress would help only about 1.1 percent of the nation's 2.2 million corporations, leaving some of the most troubled domestic manufacturers with no benefit at all, according to an analysis by the nonpartisan staff of Congress's Joint Committee on Taxation.

The new analysis is fueling a quiet war between major, profitable companies that stand to gain from $63.3 billion in reduced manufacturing income taxes over the next 10 years and old-guard steel and automobile giants that already pay little or no tax under the current system. The steelmakers and auto giants instead want the government to pay as much as 10 percent of their burgeoning health care bills by granting billions of dollars in tax credits.

The fight could imperil the most significant corporate tax legislation in 20 years if opponents convince lawmakers that the current version is cast too narrowly.

The findings "confirm my worst fears," Sen. John D. Rockefeller IV (D-W. Va.) said in a letter sent to colleagues last night. "More than 95 percent of manufacturing corporations -- the presumed targeted beneficiaries of the provision -- receive either no benefit or less than $50,000 of benefit."

Though advertised as a lifesaver for the nation's ailing manufacturing sector, the legislation would primarily benefit a handful of large corporations that have remained highly profitable during the country's long manufacturing slide -- companies such as Gillette Co., Dell Inc. and Johnson & Johnson.

Fewer than 25,000 companies would divide virtually all of the $63.3 billion in tax relief for domestic manufacturing contained in the Senate tax provision, the analysis found. Of manufacturing companies, fewer than 5 percent would benefit significantly.

The overall bill is considered must-pass legislation by lawmakers in both parties. It would repeal an illegal export subsidy that has led to punitive tariffs imposed by the European Union on U.S. exporters and replace it with a variety of tax cuts and special-interest provisions designed to ease the pain of the lost export benefit.

In fact, many more companies would benefit from the tax changes than did so from the export subsidy, which was worth about $5 billion annually to 1,886 exporters.

The Senate version, which passed in May by a 92 to 5 vote, effectively lowers the tax rate on domestic manufacturing to 32 percent from 35 percent. The House version contains a similar provision but broadens the impact by also creating a 32 percent tax bracket for any company with less than $20 million in non-manufacturing profit. The House version would ultimately lower taxes for almost all companies, but it would cost an additional $15 billion over 10 years -- a major political obstacle in the face of record budget deficits.

The Senate bill may be cheaper, but according to the committee staff's new analysis it may not be as generous as advertised. Most companies would get virtually no benefit from the corporate tax cut because most have little or no profit and thus pay little or no tax. The big winners, meanwhile, are truly big: The 500 companies that would reap the majority of the benefit have projected estimated manufacturing income of more than $4.5 trillion in 2005 alone, an average of $9 billion in profit each, Joint Tax Committee Chief of Staff George K. Yin wrote in a letter to Rockefeller.

"Had Senators been aware of this information . . . they likely would have rejected this overly narrow corporate tax cut for the 'Fortunate 500,' " lobbyists seeking to scuttle the measure wrote in private talking points.

Senate Finance Committee aides said that charge is unfair because the whole bill offers more than $167 billion in tax cuts for manufacturers over 10 years. If some businesses do not benefit from the centerpiece tax-rate reduction, they likely would benefit from other aspects.

"The Senate bill contains several provisions to help companies that are not currently profitable," said the committee's chairman, Charles E. Grassley (R-Iowa).

The findings by the Joint Tax Committee, the chief repository of tax analysis in Congress, found that the vast majority of companies would receive a tax benefit of less than $50,000, if they receive a benefit at all. But Grassley aides said a $50,000 benefit is substantial to a small manufacturer.

Rockefeller and Sen. Arlen Specter (R-Pa.) are pushing an alternative that would offer manufacturers a choice between the tax rate cut and a federal tax credit to offset health care costs. In an interview yesterday, Specter argued that this would more fairly distribute benefits by helping companies saddled with huge health care liabilities from retirees and aging workers.

"As a matter of equity, these are significant players in the economy, and it would help the economy a lot to recognize these legacy costs," Specter said.

The federal government routinely makes payments to poor individuals based on tax credits, but Senate Finance Committee aides said the government has never granted such "refundable tax credits" to businesses.

"Creating a refundable general tax benefit for businesses would cross a very controversial line, one that could have taxpayers paying for a company's ordinary business expenses," Grassley said in a statement.

But some corporations that stand to benefit little from the existing measure may be willing to scuttle the whole bill in hopes that the next go-round will prove more favorable, lobbyists close to the effort said.

All three U.S. automakers -- Ford Motor Co., General Motors Corp. and DaimlerChrysler AG -- have sent representatives to Capitol Hill to argue that the pending measure will be of more help to foreign competitors such as Toyota Motor Corp. than it will be to them.

Steelmakers also have been complaining. U.S. Steel Corp., for instance, figures that it wouldn't have benefited in 2002 or 2003 if the corporate-deduction provision were law now, because it had a net loss last year and earned only a slight profit the year before, according to Scott R. Salmon, U.S. Steel's director of government affairs.

U.S. Steel estimates that it could save $20 million in taxes a year if it could apply Specter's proposed 10 percent credit to its $200 million in retiree health expenses.

The Joint Tax Committee looked only at corporations registered as "Subchapter C corporations," the usual way major businesses file with the Internal Revenue Service. The Senate measure also applies to small businesses and partnerships, which did not fall under the analysis.

But even if the committee had looked at all those businesses, the distribution of the $63.3 billion tax benefit would not have changed much, since most of those small businesses and partnerships have small profits, tax experts said.