correction: Earlier versions of this story misstated the vote totals in the Montgomery County Council’s actions on the storm water management proposal. The article has been corrected.

Montgomery County Executive Isiah Leggett (D) (Jeffrey MacMillan)

Montgomery County Executive Isiah Leggett (D) is threatening a veto if the County Council rejects his request to privatize storm water management in Maryland’s most populous jurisdiction.

A line-item budget veto rare seen in Montgomery County, and Leggett’s promised veto of the roughly $48 million allocated to storm water management in the proposed capital improvement program budget would be the first time he will have wielded that part of his executive power.

The all-Democratic council must decide whether to go ahead with its original plan to keep storm water management mostly in-house, which it endorsed 5 to 4 in a straw vote Monday. The council could also amend its decision on the storm water management budget before a final vote on the capital budget May 24.

The veto threat had staffers dusting off their copies of the county charter for guidance Thursday. Senior legislative attorney Bob Drummer said a line-item veto could be overruled only by a supermajority — six votes on the nine-member council.

If the council doesn’t override the veto, the item disappears from the budget.

The debate about the best way to handle the county’s storm water management program has been going on for months in council committees and through memos between the council and Leggett.

It came to a head on Monday, when Leggett’s proposal — to spend $48.3 million on a contract that would address storm water runoff on 526 acres of county land — was rejected by the council in a 6-to-3 vote.

Council member Tom Hucker (District 5) put forward an alternative plan, favored by environmental groups: to continue the best storm water projects that were already in mid-design but had been halted, using the contractors that the county’s Department of Environmental Protection had been relying on for some of the work.

That proposal passed 5 to 4, with Hucker joined by Roger Berliner (District 1), Marc Elrich (At Large), Nancy Navarro (District 4) and Council President Hans Riemer (At Large). Council members Nancy Floreen (At Large), Sidney Katz (District 3), George L. Leventhal (At Large) and Craig Rice (District 2) voted against it.

“I think it’s hard for anyone to credibly argue to roll the bulk of the money into one giant contract that the public has no understanding of, that environmental groups oppose and that the council has concerns about and say, ‘Trust us,’ ” Hucker said in an interview Thursday. “That’s not the right approach.”

He said he wants to convene a working group over the summer to determine the best way to handle the storm water program going forward.

Floreen said her fellow lawmakers were micromanaging Leggett, who is in the final months of his 12-year tenure.

“It’s a very unusual situation for the council to get in the way of an executive decision to implement an improved contracting approach to delivery of solutions to problems,” Floreen said. “Mr. Leggett obviously isn’t going to put up with it. Good for him.”

Leggett said that he had become concerned with the increasing storm water management fees that county residents pay and that he felt it would be more efficient to use private contractors for more of the program.

“The council’s actions in my opinion either kicks this down the road or tries to resolve it post-next election,” he said, comparing the situation to Congress’s refusal in early 2016 to consider President Barack Obama’s nomination of Judge Merrick Garland to the U.S. Supreme Court.

“The status quo would require an ongoing increase in the fees, some levels of inefficiencies that I think are unacceptable,” Leggett said. “Council members were bowing to politics and political pressure to continue that.”