HOUSE SPEAKER Robert DeLeo expressed some uncertainty Wednesday afternoon about whether the House will be able to advance a tax package before the end of the year.

“Right now we’re still working on it. It’s still something that we’re working on,” DeLeo said after a Democratic caucus. “I would advise you to stay tuned in terms of whether we’re going to be able to cross the finish line by next week. I’ll probably know better today or maybe even tomorrow in terms of where we are.”

Next Wednesday is the last day of the year when either the House or Senate can hold roll call votes, which would almost certainly be necessary to pass a controversial bill of that magnitude.

While both DeLeo and Senate President Karen Spilka have expressed interest in boosting the amount of revenue available to fund improvements to the transportation system, neither branch has passed such a bill yet. No such bill has even emerged from committee, although House leaders have been working on a bill furiously.

If the House does not pass a tax bill next week, then practically all of the legislative action to raise taxes would need to occur during next year, an election year, when lawmakers are often more sensitive about how their decisions will affect their electability in their districts.

DeLeo’s doubt less than two weeks before the winter break stands in contrast to a statement he made in June about the House’s intentions to pour more funding into the MBTA and other transportation investments.

“Fixing the MBTA requires a long-term strategic plan as well as the long-term dedicated annual revenue to implement it. Nothing short of a modern, reliable and safe transit system is what MBTA commuters deserve, and it is what the House demands,” DeLeo said five months ago. “This fall the House plans to debate the revenue options to fund statewide transportation investments, including funding a long term strategic investment plan for the MBTA.”

Transportation Committee House Chairman William Straus and Revenue Committee House Chairman Mark Cusack have both sent strong signals that an increase in the state’s 24-cent-per-gallon gas tax would likely be part of the bill. Straus and Cusack have been working with House Ways and Means Chairman Aaron Michlewitz on the proposal.

The Greater Boston Chamber of Commerce also backs a gas tax increase, but the Associated Industries of Massachusetts says that is unnecessary, and Raise Up Massachusetts, a union-backed advocacy group found in a poll in August that the gas tax is much less popular than taxes that would tap corporations and the highest earners.

Seventy four percent of the 600 likely voters polled oppose the idea of increasing the gas tax to 39 cents per gallon, according to a short summary of the Echo Cove Research poll, which found that preventing corporate tax avoidance had broad support.

DeLeo on Wednesday wouldn’t provide an estimate about the size of the tax increase being contemplated.

“That’s one of the major issues,” said DeLeo. “I think we have to make sure what we’re going to do in terms of legislation before we put numbers out there.”

Failing to pass a tax bill to fund transportation improvements would be a major victory for conservative groups that argue the state already has enough funding on hand, and it would deal a blow to advocates who think the scale of transportation investment needs to be dramatically increased.

Spilka last week declined to commit to taking up a tax bill this session if the House passes one, even though she supports increasing revenues for transportation.

“I’ve consistently said, ‘We’ll see what the recommendations are of the chairs, and what’s the will of the senators,’” Spilka said. “I believe that we do need more revenue, so we will be taking a look at it.”

Under the state constitution, all tax bills must originate in the House but they can be amended by the Senate.