FORT WORTH — The head of the agency that regulates the oil and gas industry in Texas is asking Denton officials to withhold support from a grass-roots petition advocating a ban on hydraulic fracturing within the city limits.The university town sits on the Barnett Shale, believed to hold one of the largest natural gas reserves in the U.S. Barry Smitherman, Texas Railroad Commission chairman, called the measure “essentially a ban on drilling” that is “extremely misguided,” in a letter Thursday addressed to Denton Mayor Chris Watts and the City Council. “If other cities were to follow your lead, then we could potentially, one day, see a ban on drilling” in Texas, Smitherman wrote. City leaders temporarily halted fracking as they consider making their city the first in the state to permanently ban the practice. The temporary ban does not apply to the 275 currently active gas wells in Denton, and likewise, a permanent ban would only prevent any additional fracking from taking place, the petition’s organizers have said. “They can keep drilling, they just can’t frack,” said Cathy McMullen, a leader of the Denton Drilling Awareness Group, which submitted the petition. fracking involves blasting a mix of water, sand and an assortment of chemicals deep into underground rock formations to free oil and gas. The method has long stirred concerns about its effect on air and water quality. Industry proponents argue that fracking can be done safely and is cleaner than other forms of energy extraction. The Denton City Council plans a public hearing for Tuesday, and Watts says the letter will be added to the public record. “We’re receiving a lot of literature from both sides of the issue,” Watts said. Even if the council rejects the ban, Denton voters could still vote on it in November. Smitherman lost an attorney general’s race in March’s Republican primary.