The Appropriations Committee will need to take its budget proposal “back to the drawing board” if legislation necessary to keep it beneath the state spending cap does not find adequate support in the Senate.

The bill, approved by the committee earlier this month, prevents certain types of state spending from being counted against the spending cap. Otherwise, the proposal would exceed the cap.

But the spending cap is included in the state constitution and changes to it require a three-fifths majority to pass the legislature.

The bill is in danger of stalling in the Senate, where Democrats have a 22-14 majority. The legislation would need at least 22 votes to pass and one Democrat, Sen. Joan Hartley, voted against the bill in committee.

Sen. Toni Harp, co-chairwoman of the Appropriations Committee, said Tuesday that without the spending cap changes, the committee’s budget exceeds the cap by around $500 million.

The bill, which Gov. Dannel P. Malloy recommended with his own budget package in February, would stop counting against the cap any new spending for which the state will be reimbursed completely under a federal government program. Payments made on unfunded liabilities for both the state employee and teacher retirement systems also would be excluded.

“It’s probably the most important piece of legislation,” Harp said.

Senate Democrats plan to meet soon to discuss the bill and see where members stand on changing the cap. Harp said she hopes they find enough support to pass it.

“Either that or it will be back to the drawing board with the budget, figuring out what else we can cut,” she said. “It’s a tough position. We’re going to have a caucus on Thursday to see what people would want to do if we can’t pass it.”

Hartley, who serves as the Appropriations Committee’s vice chairwoman, said Tuesday she still has her doubts about altering the spending cap. She said she was around when the legislature approved the cap soon after the state first adopted an income tax.

“[The spending cap] was, in effect, the balancing act. So yes, I have grave concerns about it,” she said.

Hartley acknowledged the legislation needed a “supermajority” to clear the Senate but would not say whether she would ultimately vote against it. She said it was premature to speculate about the fate of the bill.

“I have to tell you, this is the budget and we’re all trying to get to the same place. I have my way of trying to get to the same place and others have theirs. We have to try to come to closure on this,” she said.

Senate Republicans have yet to meet to discuss their own positions on the bill, but Minority Leader John McKinney, R-Fairfield, said he didn’t think Democrats should expect Republican support to help pass it.

“I think it’s very unlikely that Republicans would be supportive of changes to the definition of the spending cap,” he said.

McKinney said exempting spending on unfunded pension liabilities for state employees would inaccurately depict how much spending on state workers impacts the budget and gives the majority party more room to spend money on other things.

“The spending cap has been very important in terms of putting some limit on how much state spending can increase,” he said.

In order to reach the Senate, the bill must first be approved by the House. Earlier this month House Speaker Brendan Sharkey said he expects to find the 90 votes needed to pass the bill.

Sharkey said the spending cap changes are necessary to give the state room to spend money on Medicaid, which will be reimbursed by the federal government after the program is expanded in January under the national healthcare reform law.

“I don’t think that the taxpayers of Connecticut want to see us leaving their dollars in Washington and if we do not make common sense changes to the definition of the spending cap, that’s exactly what we’re going to do,” he said.

Asked about the spending cap an unrelated press conference Monday, the governor answered generally, saying he was pleased the Appropriations and Finance Committees have so far approved budget proposals similar to his own.

“We just have to take a look at it. I’m grateful that the legislative committees have gone with a budget framework that is in keeping with the one I’ve laid out and that gives me confidence that we can get a budget done pretty quickly,” he said.