American business, typically a reliable Republican cheerleader, is decidedly lukewarm about Senator John McCain’s proposal to overhaul the health care system by revamping the tax treatment of health benefits, officials with leading trade groups say.

The officials, with organizations like the U.S. Chamber of Commerce, the Business Roundtable and the National Federation of Independent Business, predicted in recent interviews that the McCain plan, which eliminates the exclusion of health benefits from income taxes, would accelerate the erosion of employer-sponsored health insurance and do little to reduce the number of uninsured from 45 million.

That is largely the argument made in recent days by Mr. McCain’s opponent, Senator Barack Obama, who has revived a dormant campaign debate over health care with an intensified attack on the McCain plan. Conscious that the issue plays well with swing voters, Mr. Obama devoted a speech on Saturday to characterizing Mr. McCain’s plan as “radical” and a “Washington bait and switch,” and he has reinforced the message in four television advertisements.

That has set off a furious back-and-forth between the campaigns, with the McCain campaign countering that Mr. Obama’s plan also would undermine employer coverage by mandating that medium and large companies either provide insurance for their workers or pay a tax. The payments would help subsidize a new government health plan for low-income people, and some economists believe it would entice workers away from their employer-sponsored coverage.