County Supervisors bolstered San Diego’s efforts to build a new Chargers stadium on Tuesday by approving $500,000 for attorneys and financial consultants that will be needed if negotiations resume with the team.

The unanimous vote comes six days before San Diego’s stadium negotiators travel to Chicago on Monday aiming to convince a panel of NFL owners that the Chargers should stay in San Diego instead of moving to Los Angeles.

San Diego officials have frequently touted the strong financial partnership forged this year between the county and city on a potential new stadium, so it would have been a setback if the supervisors hadn’t approved the money on Tuesday.

The approval comes one day after St. Louis officials got a boost on their stadium efforts when a judge ruled on Monday that the city won’t need voter approval before spending tax money on the project.

The Chargers, Oakland Raiders and St. Louis Rams are all pursuing stadium projects in the Los Angeles area, prompting officials in each of those cities to explore local stadium proposals that could help them keep their teams.

Tuesday’s vote increases the county’s contribution to the stadium effort from $250,000 to $750,000, but Supervisor Ron Roberts stressed that the additional money won’t be spent unless the city’s impasse with the Chargers over environmental issues is resolved.

“Should they decide they are willing to come back to the bargaining table, then we will be in a position to bring our team together and continue the negotiations,” said Roberts, who has led the county’s stadium effort. “I appreciate my colleagues’ unanimous support for this item.”

Roberts, however, said he was discouraged by recent developments on the stadium front.

“I don’t have anything significant to report in the way of progress, maybe just the opposite,” he said.

That comes one week after San Diego’s negotiators spent three hours updating several top NFL officials about the city’s recent stadium progress, particulary an accelerated environmental analysis that could make a Jan. 12 public vote on a financing plan possible.

Roberts blamed the Chargers.

“We’re seeing a lot of attempts to confuse the issue and to belittle efforts that are being made,” he said.

Roberts said he was particularly disappointed by a letter attacking the city’s efforts that was initially described as an NFL document, but which turned out to be written by Chargers officials.

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The letter cast doubt on the legality of the accelerated environmental analysis and whether the county would participate in funding the stadium as expected.

It also said the city has exaggerated how much Assembly Speaker Toni Atkins can accelerate stadium-related litigation, stressing that some of the potential lawsuits would be outside of the state Legislature’s reach.

Chargers special counsel Mark Fabiani said Tuesday that the document was prepared by the Chargers to provide background information for reporters before last week’s meeting between the NFL and San Diego’s stadium negotiators.

On a positive note, Roberts said he and Mayor Kevin Faulconer expect to meet in October with NFL owners in New York City.

Roberts and Faulconer won’t travel to Chicago with their negotiating team for Monday’s presentation, which Faulconer spokesman Matt Awbrey described as a 45-minute technical presentation.

Lead negotiator Chris Melvin, a New York City attorney, will make that presentation to the NFL’s relocation committee — six owners focused on the Los Angeles situation.

The additional $500,000 from the county comes after city and county officials agreed in April to spend $250,000 each on consultants and lawyers.

That team led negotiations with the Chargers before they broke off talks in mid-June, and has continued to help as San Diego’s efforts have shifted toward working directly with the NFL.

The City Council approved an additional $2.1 million on July 14 to hire consultants needed for the accelerated environmental review, so the county has agreed to handle extended funding for the stadium negotiators if talks resume.

“In partnership with Mayor Kevin Faulconer, we have assembled the best team you could ask for to negotiate a stadium financing plan that is fair to all parties,” Roberts said.

He stressed that the additional money won’t be spent unless there is progress with the Chargers.

“This doesn’t lock us into anything,” he said. “It doesn’t even mean there are going to be any negotiations, unfortunately. I can assure you any type of agreement that results will be back before this board.”

Supervisor Dianne Jacob said the lack of obligation was part of the reason she supported the additional money.

“It doesn’t commit the county to any type of stadium proposal or financial agreement between the county and city,” she said. “A stadium proposal has not been agreed to by all the parties, and who knows if it ever will.”

The additional money comes from the county’s Neighborhood Reinvestment Program, which provides grant funds to county departments, public agencies and to nonprofit community organizations for one-time needs.