LONGMONT, Colo. — This northern Colorado city vaulted onto the front lines of the battle over oil and gas drilling two years ago, when residents voted to ban hydraulic fracturing from their grassy open spaces and a snow-fed reservoir where anglers catch smallmouth bass.

But these days, Longmont has become a cautionary tale of what can happen when cities decide to confront the oil and gas industry. In an aggressive response to a wave of citizen-led drilling bans, state officials, energy companies and industry groups are taking Longmont and other municipalities to court, forcing local governments into what critics say are expensive, long-shot efforts to defend the measures.

While the details vary — some municipalities have voted for outright bans, and others for multiyear suspensions of fracking — energy companies in city after city argue that they have a right to extract underground minerals, and that the drilling bans amount to voter-approved theft. They also say state agencies, not individual communities, are the ones with the power to set oil and gas rules.

Because the cases are being fought one by one at the state level, they are not expected to set any immediate nationwide standard on whether homeowners and local leaders have the power to keep drilling rigs out of their towns. But they are being watched as legal litmus tests as more governments plunge into the acrimonious debate over fracking, the process of pumping huge amounts of water, sand and chemicals underground to release oil and gas buried in shale rock.

New York State’s move to ban fracking last month, for example, was foreshadowed by a ruling in June by the state’s highest court that towns could use their zoning laws to outlaw the practice. In the wake of New York’s announcement, anti-fracking activists in California, Maryland and Pennsylvania, among other states, renewed their calls for bans.

Citizens’ groups and environmental organizations say residents have the right to live on suburban streets and walk their children to school without worrying about methane leaks from wellheads, or traffic and noise from the drilling rigs and tractor-trailers that haul machinery and water to fracking sites. Other property owners and residents, of course, embrace fracking as an economic powerhouse that has provided thousands of jobs, enriched local governments and opened new economic opportunities in rural communities.

Here in Colorado, the energy industry, which argues that cities lack the authority to outlaw fracking, has already won rulings overturning three fracking prohibitions.

“You have to take a hard line on this,” said Tisha Schuller, president of the Colorado Oil and Gas Association, which is leading the charge to strike down the regulations here. “A ban does not address our underlying energy needs. It clarifies the agenda of activists, which is, ‘We don’t want any oil and gas development, although we as a community will continue to consume oil and gas.’ ”

Ms. Schuller added, however, that her group’s “overwhelming priority” was working with communities, not suing them. To that end, she said, it has helped forge more than 20 agreements between energy companies and communities across the state that seek to balance concerns about noise, traffic and other side effects of drilling with the right of property owners to tap their mineral resources.

Longmont, which sits near the juncture of rolling plains and jagged mountains, has spent about $136,000 fighting — unsuccessfully so far — to defend a 2012 measure that outlawed fracking. In July, a district court judge tossed out the ban, and the city is appealing.

A judge also overturned a fracking ban last year in Fort Collins, Colo., and denied pleas from the city to keep the ban in place while local officials went to court to defend a five-year fracking moratorium. In Broadview Heights, Ohio, energy companies are suing the town — and residents are suing the energy companies in return — over a bill of rights that outlawed fracking and the disposal of its byproducts.

In Denton, Tex., one day after voters passed the state’s first ban on fracking in November, the measure was met with lawsuits from the Texas General Land Office and the Texas Oil and Gas Association. An official on the commission that regulates oil and gas in Texas told The Dallas Morning News that she would still issue permits to companies hoping to drill in Denton, even while the ban remained on the books.

In Longmont, energy companies and fracking opponents had skirmished before over plans to drill near new subdivisions and a golf course. But in 2011, opposition grew widespread after residents learned of a proposal to drill near Union Reservoir, a glassy lake that reflects the mountains. In November 2012, a campaign by environmental groups led to a ban not only on fracking, but also on the storage or disposal of any fracking waste.

“People thought it was quixotic,” said Kaye Fissinger, a retired Longmont resident who managed the campaign. The industry spent about $500,000 on commercials and brochures that year, more than 10 times what the activists raised to pass the ban. But, Ms. Fissinger said, “ ‘Impossible Dream’ has always been one of my favorite songs.”

Much more than $500,000 was at stake. City officials and energy companies estimated that Longmont was floating atop as much as $500 million of oil and gas — resources that were locked away. While the ban did not explicitly outlaw drilling, industry officials said the prohibition on fracking removed a crucial step needed to tap the oil and gas.

“There’s absolutely no question that what the city did is illegal,” said Dale Bruns, a consultant for TOP Operating Company, the main oil and gas operator in Longmont, which is suing the city. “Longmont just repeatedly shoots itself in the foot. You’ve got a bunch of people who are just adamant that fossil fuel is bad, and it’s terrible for Longmont. This minority group has fired up the public with false claims.”

Bryan Baum, a former mayor who opposed the ban, predicted that it would fall at every level of appeal, including at the Colorado Supreme Court, because only the state can regulate drilling. Now, as the case heads to higher courts, Mr. Baum said he believed many in town were developing buyer’s remorse about the ban.

“If we took that same vote, I think it would come out differently,” he said. “It’s cost the city a lot. It’s not just the money that it costs to defend these — it’s the opportunities and the industries it could’ve brought to our community.”

While the Longmont City Council voted unanimously in August to defend the fracking ban, other towns have decided it is just too costly a fight. After Lafayette, Colo., lost an initial legal judgment on its voter-approved restrictions on oil and gas development, the Council voted, 4 to 3, to give up and drop further appeals.

There are only about 12 active wells in Lafayette, leftovers from the 1980s, but the community sits on the fringe of Colorado’s oil boom and wanted to make sure the drilling did not encroach. Even though the ban was largely symbolic, it drew a quick challenge from the Colorado Oil and Gas Association and was overturned. After that battle, which cost $62,000, the Council members had had enough.

“It’s a scare tactic,” said the mayor, Christine Berg, who voted to continue the legal case. “We’re a small community. We’re 25,000 people, and we’re fighting this battle. We’re stuck between these legal threats and what our constituents want, which is a say in the future of their communities.”

Originally published by The New York Times