The Senate Budget Committee passed on Thursday night a federal budget resolution, which the panel’s lead Republican charged provides incorrect estimates for war funding.

The Democratic-led panel approved its 10-year, largely-symbolic blueprint for federal spending after two days of debate. The GOP-run House Budget Committee approved its contrasting budget resolution earlier in the day Thursday, setting up contentious House and Senate floor battles next week over thorny matters including “sequestration” budget cuts, taxes, Medicare and health-care reform, and stimulus spending.

During the Senate Budget Committee’s markup session Thursday, Ranking Member Jeff Sessions (R-Ala.) argued the resolution crafted by Senate Democrats would not actually reduce the deficit by $1.85 trillion over a decade, as committee Chairwoman Patty Murray (D-Wash.) claimed. Sessions zeroed in on the war funding–for “Overseas Contingency Operations” (OCO)–in the resolution. It proposes $100 billion in OCO funding for FY ’13, which is what the Pentagon requested. Then, citing President Barack Obama’s strategy to end the war in Afghanistan by the end of 2014, the Senate Democratic plan calls for only $50 billion in OCO funding in FY ‘14 and $25 billion in FY ’15.

“Reserve funding is available for OCO needs after 2015, to meet the needs of the president’s strategy,” the resolution says. “The (reserve) fund is also available to ensure fiscal responsibility with respect to unforeseen or ongoing OCO costs.”

A Democratic staffer said the president would need to justify the need for more OCO funding after 2015, and any needed funding would be paid for through measures such as spending cuts and revenue.

“Of course he could ask for more and Congress can give more, but you don’t budget for any more,” Sessions argued. “You budget zero for eight years….Well, we disagree with that….And I would suggest…that’s about a…$400 billion incorrect assumption.”

Sessions further argued that the sequestration cuts are “current law” and should be factored differently into the Senate resolution. He said cancelling sequestration would “amount to about $1.1 trillion in new spending.”

The Senate Budget Committee’s proposal calls for ending the $500 billion in across-the-board “sequestration” cuts to defense over a decade but keeping roughly half that amount–$240 billion–in other Pentagon reductions. The House plan, by contrast, would keep the sequestration cuts, which started March 1 and total more than $1 trillion over a decade when defense and non-defense spending are counted. Yet the House panel’s resolution says for defense spending over the next decade it has “approximately $500 billion more than will be available absent changes in the Budget Control Act,” referencing the law that created sequestration.

The House and Senate resolutions include a raft of contentious proposals, with the House plan calling for balancing the federal deficit over the decade with $4.6 billion in budget cuts, a Medicare overhaul, and cancellation of parts of Obama’s health-care reform. The Senate proposal seeks $975 billion in new tax revenues along with $975 billion in budget cuts and $100 billion in stimulus spending, and would not attempt to balance the budget.