A plan could soon be in place to boost funding for the state's transportation system with $500 million in new taxes, but it might come without the blessing of Gov. Deval Patrick.

Patrick had barely finished outlining the amendment he will file to the Legislature's transportation financing plan on Tuesday when House Speaker Robert DeLeo and Senate President Therese Murray rejected the proposal that would replace expiring Massachusetts Turnpike toll revenue with a 3-to-5-cent gas tax increase.

With Patrick indicating he can't support the financing plan as written, DeLeo vowed to seek an override of a veto, if necessary, and pointed at the strong support in the House for the compromise bill to indicate Democrats should be able to muster the votes needed to implement the plan without Patrick's signature.

The plan is critical to future transportation investments, but is also needed to balance the fiscal 2014 budget and avoid the need for fare increases and service cuts at the MBTA. Transportation Secretary Richard Davey said the T was "not pushing the panic button" just yet. "Calamity is not in the future at this point," Davey said.

Patrick acknowledged that the transportation bill and the $34 billion budget bill are intertwined, and said he's preparing for every outcome. Patrick must act on the budget in 10 days, or by Thursday, July 11, and DeLeo offered no timetable to address the governor's amendment, although no formal sessions are scheduled this week.

Though he declined to predict whether he would have the necessary votes to override, DeLeo pointed to the 106 members who supported the bill in the House last week and a few who were absent, but who he believes will support the Legislature's plan.

"The numbers that have been passed, the numbers that have been stated in our revenue package are real numbers. They're not fictitious. It will get the job done that all three of us want to get done and I see no reason for me, as the speaker of the House, to ask the membership of the House to vote for a further gas tax increase," DeLeo told reporters.

Patrick's amendment would trigger an automatic increase in the gas tax in 2017 if Massachusetts Turnpike tolls come down as currently scheduled. Though he said he would prefer to see the tolls replaced with another source of revenue, Patrick said he's open to keeping the tolls up or using something other than the gas tax to replace the $135 million in toll revenue.

The state currently collects about $33 million for every cent added to the state's 23.5-cent gas tax, requiring a 4-cent or 5-cent increase to replace the toll money, according to Davey.

The Legislature last week approved a five-year transportation financing plan that would raise $500 million in new taxes, including a 3-cent increase in the gas tax, a $1 per-pack hike in cigarette taxes and new sales taxes on software design services that critics say will harm the state's innovation industries.

House and Senate leaders say the plan would direct as much as $805 million in new spending to the state's aging infrastructure and public transit systems by 2018, but Patrick has expressed concern that with tolls on the turnpike from Newton to the New York border due to come down in 2017 the total will be far less. The administration estimates $135 million in toll revenue will disappear when the tolls come down.

"The bill counts toll revenue from the western turnpike even after the tolls are scheduled to come down. As a result it will never produce $800 million in new transportation funding," Patrick said.

The governor shied away from using the word "veto" during his remarks, but repeatedly said he would not support the bill in its current form. It's possible that Patrick could let the bill become law without his signature.

"I cannot accept less than $800 million and further compromise the needs of our transportation system. And I will not tell people this bill raises $800 million for transportation when it doesn't. To me this last point is a matter of public trust," Patrick said.

The governor said he's already compromised given the estimated $1.2 billion needed to improve and maintain transportation systems, and worried that anything smaller than $800 million will jeopardize projects outside of Boston and threaten "regional equity."

During his afternoon press conference, Patrick seemed optimistic about the prospects for a compromise with the House and Senate. "There are an awful lot of people in and out of this building who want me to wink and nod and act like it's an $800 million bill. It's not. It can be, and we're almost there," he said.

But with him still at the podium fielding questions when House and Senate leaders issued a statement rejecting the proposal, Patrick said, "People say a lot of things in this building and then we get to where we need to get to, so I'm not going to worry about that."

Patrick said his staff had already begun to reach out to members to discuss his amendment and concerns, which raises questions about whether progressive Democrats who opposed an earlier House bill because it did not generate enough new revenue could be persuaded to sustain a veto.

The House voted 106-47 in favor of the financing deal reached by the House and Senate, while the Senate voted 34-6 in favor. If all 156 current House members vote, DeLeo would need to round up 104 votes to override a veto.

Though some lawmakers have suggested the issue of tolling doesn't have to be addressed immediately, Patrick said projects like the Green Line extension require long-term borrowing and investors need certainty that the funding will be available to pay the bonds.

DeLeo called it "very premature" to be worried about toll revenue beyond 2017 considering the Legislature has asked for a review of tolling, including the potential for border tolls. The Speaker also said he doesn't believe the Massachusetts Department of Transportation even needs legislative approval to keep the turnpike tolls operating.

The Winthrop Democrat said the law from the middle of last century called for the tolls to be removed when the bonds on the highway were paid and if financing was no longer needed to keep the road in a state of good repair.

Republicans quickly scoffed at Democratic leaders like Murray and DeLeo contending they opposed another gas tax increase because it "threatens working families and businesses still fighting to overcome the financial downturn."

"While it is nice Democrats agree with House and Senate Republicans that families across the Commonwealth are struggling, their decision to push a myriad of crippling taxes, including a technology tax widely panned as a job destroyer, shows just how disingenuous Beacon Hill Democrats really are," MassGOP Chairwoman Kirsten Hughes said.

In their joint statement, Murray and DeLeo said, "Last week, the Legislature passed a carefully calibrated revenue proposal that solves long-standing financial problems within the transportation system. The administration's proposal tying the question of tolls in Western Massachusetts - a plan not even mentioned in its original bill - to a 4 cents gas tax increase places too high a burden on the taxpayers of our state. This threatens working families and businesses still fighting to overcome the financial downturn. Therefore, we will ask our respective chambers to reject the administration's proposal."