Like other golf courses across America, the Chevy Chase Club in suburban Maryland is caught up in the ancient battle between man and weeds. The club recently informed its members of a major offensive against ugly patches of invasive grass that impede a ball’s roll toward the hole on their velvety greens.

But its preferred method of killing weeds involves a controversial pesticide called methyl bromide, which the Environmental Protection Agency barred most organizations from using years ago.

Methyl bromide chokes weeds down to their roots and wipes out other pests such as termites. But the odorless gas also contributes to thinning the ozone, and high doses can have serious health effects. The EPA started phasing it out in 1995 as part of the Montreal Protocol on ozone-depleting substances.

Although manufacturers were banned from producing methyl bromide in 2005, and contractors were barred from using it for most purposes, groups such as the Golf Course Superintendents Association of America and farmers lobbies fought successfully for a “critical-use” extension. No other fumigant is as effective, they argued.

Golf courses are allowed to use methyl bromide until December 2013, but they can only draw from supplies that were stockpiled before 2005. About 36 million pounds of methyl bromide was available in 1995, according to the Natural Resources Defense Council. About a third of that was used as it was phased out over 10 years, leaving about 25 million pounds.

Now, as the exemption period comes to a close, the Chevy Chase Club is one of many golf courses that groundskeepers and experts say are hurrying to use the remaining supply on weed-pocked courses before a total ban, worrying environmentalists.

In a newsletter to members, Chevy Chase Club President Thomas F. Fitzgerald said the board approved the use of methyl bromide so that it can be used before the EPA’s deadline. The golf course’s greens are expected to start deteriorating shortly after the deadline, but a restoration using the gas will preserve them for up to 15 years.

“In light of these circumstances, the board has authorized that we move forward with redoing the . . . greens” before the cutoff, according to Fitzgerald’s letter.

The club is under no obligation to inform its neighbors in the densely populated enclave near the District line of its use of the odorless gas, and no permit is required, according to the Maryland Department of Agriculture, which regulates the use of pesticides. A club member anonymously provided a copy of the letter to the Environmental Working Group, a research and advocacy organization, which forwarded the letter in an e-mail to The Washington Post.

Methyl bromide is applied by professional contractors in protective clothing, said golf superintendents and experts who study turf. “You don’t want to mess with this stuff,” said Terry Buchen, a master greenskeeper and golf course consultant in Williamsburg. “It’s a very lethal gas. They contract it out.” But Buchen said that he strongly believes its use on golf courses is safe.

The pesticide is injected into the ground, which is then covered with a tarp for up to 72 hours. But the gas wafts into the atmosphere as a vapor.

A three-day buffer zone is recommended to protect humans and pets. Like all pesticides, methyl bromide washes into nearby waterways when it rains. Environmentalists say it should have been completely banned years ago.

“The U.S. is the only nation that’s using this pesticide,” said Sonya Lunder, a senior analyst for the Environmental Working Group. “The U.S. uses 80 percent of the agricultural permissions for methyl bromide” with exemptions allowed under the protocol, Lunder said.

“There’s this issue because it vaporizes out of the ground and it travels. . . . It can drift into the areas around it, where people who aren’t wearing protective equipment are exposed,” Lunder said.

Reports by state agricultural departments say that it can be lethal if ingested in high doses.

Methyl bromide is favored by groundskeepers at many major golf courses, particularly in southern climates where weeds are more aggressive, experts said. The Congressional Country Club in Bethesda, which hosted this year’s U.S. Open, applied it in 2009, a groundskeeper said.

Other area golf courses were contacted by The Washington Post to determine if they also use the pesticide, but voice-mail messages were not answered. A spokesman for the Golden Horseshoe Golf Club at Colonial Williamsburg said that course does not use methyl bromide.

Suzy DeFrancis, a member of the Chevy Chase Club’s board of governors, said the fumigation will probably begin under a licensed contractor next spring. DeFrancis said the board researched the gas, determined that it was safe, and felt no need to notify area homeowners. The club has used the gas on numerous occasions in the past with no reports of adverse effects, she said.

Several members of the Chevy Chase Club have inquired about its plans to use the gas, but none have taken up the club on its offer to discuss the matter further, DeFrancis said.

“If neighbors have concerns, we’re happy to share information with them,” she said. “We take environmental stewardship very seriously at our club.”

Farms, which use the vast majority of the pesticide to prepare soil for crops, have encountered some protests from farm workers, nearby homeowners and, in at least one case, the federal government, about its toxicity. Golf courses, which use only 1 percent of methyl bromide worldwide, rarely receive complaints from golfers or nearby residents, experts said.

A year after the phaseout of methyl bromide began in 1995, the California Department of Pesticide Regulation released a report showing that the pesticide lingers in unsafe levels around homes that are fumigated. Hazardous vapors can drift through empty pipes into neighboring houses, the study said.

Methyl bromide levels can be several times higher than what is safe, the study said. Nearly 600,000 pounds of the pesticide was used to fumigate California homes and businesses in 1995, often to control termites.

In August, the EPA’s civil rights division settled a 12-year-old discrimination lawsuit it filed against the California Department of Pesticide Regulation, which said it put Latino children at risk by allowing methyl bromide to be applied in unhealthy levels near a school.

As part of the settlement, the state agreed to dispatch regulators to monitor pesticide levels near the school. The EPA said the students were at risk, but it could not prove that the level of application caused health problems.