The Biden administration said it would spend more money to research cattle diets and expand gas-capturing manure-disposal systems for farmers to voluntarily reduce methane emissions, after supporting more than $200 million in such projects last year.

But it hasn’t proposed any new air-pollution regulations targeting the agricultural sources.

“We’re taking a look,” Environmental Protection Agency administrator

Michael Regan

said when asked recently about regulating methane from agricultural sources. “You know, I can’t promise that we’re going to have anything this year, but it’s on the menu.”

Beef and dairy cattle, along with pigs and other farm animals, contribute roughly 27% of methane emissions in the U.S., according to the EPA. Most of that comes from their belching; livestock manure accounts for an additional 10% of methane emissions.

That puts agriculture on par with the energy industry in methane emissions, with natural gas and petroleum generating 30% and coal mining 10%.

Some environmentalists say the Biden administration is going easy on big agriculture to avoid a bruising political battle with the powerful farm lobby. Agricultural groups say reducing methane from cattle isn’t as simple as plugging leaks from pipelines and oil wells.

Oil-and-gas industry groups haven’t pressed for methane regulations on agriculture, in part because they don’t want to antagonize lawmakers in rural districts, who often represent both energy companies and agribusiness, according to people familiar with the situation.

Mary-Thomas Hart, environmental counsel for the National Cattlemen’s Beef Association, said the group would lobby against Clean Air Act regulations until measuring methane discharges from livestock becomes more precise.

She said voluntary measures, such as restoration of grazing areas with carbon-absorbing plants, are the best way for the industry to lower carbon emissions.

“Regulating farmers and ranchers out of business isn’t the answer if you want to continue” those carbon-reducing farming practices, she said.

Environmentalists say that despite the challenges, there is an urgent need to curb emissions of methane, a potent greenhouse gas.

While carbon dioxide is considered the biggest global warming contributor, methane traps roughly 85 times as much heat. Global leaders at the Glasgow climate summit last year made cutting methane emissions a priority, with the U.S. and dozens of other countries pledging to cut emissions by 30% by 2030.

“The Biden administration has talked often about the importance of cutting methane and has imposed new methane restrictions on the energy sector, but they’re simultaneously giving a free pass to agriculture,” said

Viveca Morris,

executive director of the Law, Ethics & Animals Program at Yale Law School.

The Sierra Club and other environmental organizations, led by nonprofit watchdog group Public Justice, petitioned the EPA last year to regulate methane emissions from big dairy and hog farms.

“The window for taking action is short,” Sierra Club attorney

Andres Restrepo

said. “We have to do everything we can to address these emissions.”

Methane from manure and digestion has grown 19.3% since 1990, mostly because more farmers are mixing manure with liquid for disposal. Emissions from oil and gas, which face new regulations estimated to cost producers $1.5 billion by 2026, have fallen 17%, according to the EPA.

Policy makers in favor of more serious, enforceable regulations could face headwinds from the powerful farm lobby. That consortium of groups has the backing of well-resourced global producers such as

Tyson Foods Inc.,

Archer Daniels Midland Co.

and Cargill Inc.

The agriculture lobby has spent about $704 million in the past five years to influence policy makers on a range of issue including greenhouse-gas emissions, according to statistics compiled by OpenSecrets, a nonpartisan watchdog group.

The lobby can also mobilize grass-roots campaigns quickly in nearly every rural Congressional district, where agriculture is often a major employer and economic engine, said

Ben Lilliston,

director of rural strategies and climate change for the Institute for Agriculture and Trade Policy, a Minnesota nonprofit that tracks emissions from agribusiness.

“I think Biden and the Democrats are reluctant to step up to really change agribusiness and the big agriculture lobby because they are worried about offending them and potentially losing support in rural America,” Mr. Lilliston said.

Congress isn’t weighing any proposals that include regulations on agricultural methane. Some lawmakers support voluntary financial incentives for ranchers and farmers to cut methane emissions.

Rep. Ro Khanna

(D., Calif.) said Congress should consider stronger emissions standards as an option for cutting methane. “But anything we do should consider the voices of family farmers across the country,” he said in a statement.

Farmers and agricultural researchers say there are no easy solutions.

“I’m optimistic, but I’m also cautioning the farming community not to wait for a silver bullet,” said

Frank Mitloehner,

a University of California, Davis researcher who has tested natural ingredients such as garlic as feed additives to reduce methane from cows.

European Union food-safety regulators in November approved the use of the chemical Bovaer, which can cut belched methane from beef cattle by up to 80%. Its Dutch manufacturer,

Royal DSM

NV, is hoping to win U.S. approval.

Another possible solution calls for attaching rubber masks above cow nostrils to neutralize methane emissions. Cargill is preparing to put the devices, from London startup Zelp Ltd., on dairy cows in Europe later this year.

Francisco Norris,

Zelp’s chief executive officer, said the devices aren’t widely available yet.

For manure, farmers are increasingly putting waste into covered lagoons or silo-like devices called digesters that capture methane that can then be sold as fuel.

But the systems can cost millions of dollars, and EPA records show fewer than 300 digesters operating on U.S. dairy farms.

“My question to society is, ‘Are you willing to pay for that?’ ” said

Bryan Sievers,

an Iowa farmer with a 2,400-head cattle feedlot.

Mr. Sievers used federal grants to build a $7.3 million digester system, and recently joined with developers on a $14 million expansion and pipeline that will enable him to sell methane to utilities.

“Because of the extremely high cost of these projects, most farms can’t do it on their own,” he said.

Marilyn Hershey

built a $3 million digester system for manure at her 800-cow dairy farm outside Philadelphia, using grants and savings.

But she still worries that regulators will mandate costly methane rules for farms.

“The fear is that someone from Washington is going to make a decision even though they’ve never been on a farm, and that’s not right,” she said.

U.S. Department of Agriculture officials say they’re counting on market incentives, funding and research, not mandates, to curb cattle methane.

“We’re confident we can make a lot of progress over the course of the decade,” said

Bill Hohenstein,

the USDA’s director of Energy and Environmental Policy.

—Timothy Puko contributed to this article.

Write to Katy Stech Ferek at katherine.stech@wsj.com