The District owns the ballpark, and the Nationals pay $5.5 million annually in rent. (Greg Fiume/GETTY IMAGES)

Mayor Vincent C. Gray said Tuesday that Washington Nationals owner Theodore N. Lerner pitched him earlier this year on a pricey plan to have the city build a retractable roof over Nationals Park — a proposal, Gray said, that he swiftly but politely rejected.

The private one-on-one meeting took place in the John A. Wilson Building in mid-July and lasted about 15 minutes, Gray said.

“What Lerner wanted to talk about was the possibility of a roof on Nationals Park,” the mayor (D) said. “That was it. There was no discussion about how much it was going to cost and no further details. I’ve had no further discussions.”

An administration official familiar with the matter but not authorized to comment publicly on it confirmed that there have been no recent talks about improvements of that scope for Nationals Park, which was built with well more than $600 million in taxpayer financing and opened in 2008.

“The mayor was polite but unequivocal,” the official said. “We are not going to spend taxpayer money to put a roof on the stadium, regardless of the cost.”

A Nationals spokeswoman did not reply to a request for comment Tuesday evening.

The meeting was publicized Tuesday after WNEW (99.1 FM) reported that team executives had approached several city officials about building the roof.

The proposal was apparently not widely circulated. Gregory A. O’Dell, the president and chief executive of Events D.C., the city government commission that oversees the ballpark, said Tuesday that any plans for a roof were “complete news to me.”

Two other officials who keep close tabs on sports-related matters — D.C. Council member Jack Evans (D-Ward 2) and William Hall, a member of the Events D.C. board of directors — also said they were unaware of the proposal.

The team has priced the roof at $300 million, the official said, but that number appears speculative.

Gray said he was unaware that the roof could cost so much and wondered why the issue had come up again now, months later. City officials later researched the issue, Gray said, and found that adding roofs to existing stadiums after the fact was unusual. He also said he looked at sketches the Nationals provided. “I’m not prepared to go ask the city for $300 million,” he said. “Getting the stadium done in the first place was hugely controversial. And now a roof? I’m not prepared to do that. I’m concerned about hurting the aesthetics of a beautiful stadium.”

A third city official cited multiple doubts about the plan’s workability. One, that official said, was that it would probably cost far more long term because of the cost to heat and cool the park once it had a roof. Another was the aesthetics: “The stadium wasn’t designed for a roof, and to put one on now would be cost-prohibitive.”

The District owns the ballpark, and the Nationals pays $5.5 million in yearly rent as a tenant. The team’s stadium lease obligates the city to pay for “necessary” capital improvements to the stadium over the course of its 30-year term. But officials familiar with the lease said it was highly doubtful a roof could fit into that category. And should the Nationals want to add a roof to the ballpark with their own funding, they would need approval from the city.

Adam Kilgore and Jonathan O’Connell contributed to this report.