A Baton Rouge-based research group accused the Jindal administration of using revenue numbers that could knock the budget neutrality of the governor’s tax plan out of balance by at least $500 million.

The Public Affairs Research Council of Louisiana also concluded that middle and upper income taxpayers would get a tax break under the plan, with the biggest tax benefits going to taxpayers with the highest earnings.

“The losers in the tax swap deal need to be identified and the impact on them needs to be explained more fully,” PAR said in a nine-page commentary.

Tim Barfield, executive counsel for the state Department of Revenue, disagreed with PAR’s assumptions.

He said the plan will be revenue neutral.

“A standard approach to estimate the future is to begin with the best data as of today. This we have done, but only as the starting point. The Legislative Fiscal Office and other economic experts agree with our methodology,” Barfield said in a prepared statement.

“As this debate begins, if we want to see truly revenue neutral balance, we think some adjustment needs to be made,” PAR President Robert Travis Scott said after a presentation featuring the Tax Foundation officials who helped the Jindal administration put together the tax overhaul package. The lecture by Joseph Henchman and Scott Drenkard was part of an LSU Public Administration Institute meeting.

Scott said PAR, a membership group that researches public policy issues, questioned some of the numbers presented by the administration. For instance, the plan reflects personal income tax numbers from a couple years ago when the economy was coming out of recession, so they were lower than they would be now, he said. At the same time, the plan uses sales tax collections that reflect a more healthy economy, he said.

“We’re not saying the plan is impossible. We’re saying the initial numbers need to be adjusted to reflect a truly revenue neutral picture,” Scott said.

Gov. Bobby Jindal wants to eliminate the state’s personal income and corporate taxes in favor of increasing the state sales tax to 5.88 percent and taxing more services. The governor contends the plan will be revenue neutral, allowing state government to still pay the bills that keep colleges, hospitals and other public services operating.

The proposal will be debated in the legislative session that starts April 8.

The budget neutrality of the plan is important to many legislators after back-to-back years of state spending cuts. Some already are uneasy about making dramatic changes to the state’s tax structure in a short window of time. The plan would kick in Jan. 1.

PAR said the Jindal administration’s numbers are off by several hundred million dollars because 2011 recession-influenced revenue figures were used.

For example, $2.7 billion in personal income taxes needs to be replaced, not the $2.4 billion cited by the Jindal administration, PAR said.

The administration appeared to use “lower figures of the past to count the costs” and “higher figures of the future to count the benefits,” the research organization said.

“The use of income tax figures that were depressed by the economic downturn two years ago, as opposed to the trend of recovery and higher revenues that the state is experiencing currently, can result in the plan not being revenue neutral,” PAR said.

The organization said the plan could be $500 million to $650 million short of revenue neutrality.

Also simmering is an argument over who the winners and losers would be in the tax plan.

The Jindal administration contends “the vast majority of Louisiana taxpayers will save more through the elimination of state income taxes than they will pay in increased state sales taxes.”

Administration aides promoted a scenario in which “teachers making $45,000 per year filing individually would see their annual state tax burden reduced by more than $800 on average.”

PAR said someone has to pick up the tab.

The organization said businesses could be losers if they heavily use services that now would be taxed.

Mark Ballard of the Capitol news bureau contributed to this report.