A Montgomery County lawmaker is urging the county to help residents prepay their property taxes before the end of the year, a move that seeks to dodge certain impacts of a Republican-backed federal tax plan but could be tricky to enact.

In a memo to Montgomery's chief administrative officer, Timothy Firestine, council member Roger Berliner (D-Potomac-Bethesda) noted that the tax bill — which edged closer to passage Tuesday — allows homeowners to prepay their local property taxes.

The tax plan, which, if passed, could take effect as early as Jan. 1, also would cap deductions for state, local and property taxes at $10,000, a significant blow to wealthy homeowners in expensive jurisdictions such as Montgomery.

If residents pay their property taxes before the law takes effect, they could avoid the cap for one more year, Berliner said, potentially saving big bucks for those whose homes are worth millions.

Passage of the bill would be a major win for President Trump and congressional Republicans, who are aiming to send legislation to the Oval Office by Christmas. Democrats and other critics say the overhaul disproportionately favors corporations and the very rich, and would dangerously increase the deficit.

State law allows Maryland counties to enact prepayment legislation, county officials said. But the council is out of session until mid-January, meaning any local law would have to be passed next month and implemented retroactively.

Such a move would be rare, Berliner said, but isn't out of the question.

"It's one way we can show our residents that we have their backs in the face of larger income tax liability at the federal level," Berliner said.

Berliner said he expected that the all-Democratic council would unanimously support a retroactive prepayment law when it reconvenes in the new year.

He described the cap as particularly harmful to Montgomery County residents "because property values in our county are so significant, and so property taxes are generally significant as well."

With the end of 2017 fast approaching, Montgomery officials were in a frenzy Tuesday over how they would be able to quickly enact a prepayment option and find ways of alerting residents.

Firestine said that in addition to passing a new county law, there would be administrative tasks to sort out associated with it, such as getting instructions out to residents and tracking early payments.

Officials acknowledged that the council didn't have much time but said it was important to make the prepayment option available.

"We're doing this in real time," Berliner said.