Scott James/The Bay Citizen

Fort Funston park in San Francisco, a popular destination for dogs and their caretakers to explore the dunes

A line has been drawn in the sand dunes.

In the Golden Gate National Recreation Area in Marin, San Francisco, and San Mateo Counties, two passionate adversaries are facing off: animal lovers against, well, more animal lovers.

Proposed rules could ban dogs or require them on leashes in the national recreation area, a bounty of land controlled by the National Park Service that includes the Marin Headlands; Crissy Field, Ocean Beach and Fort Funston in San Francisco; and Milagra Ridge and Mori Point on the Peninsula.

Dogs currently run loose in many areas, but that practice could end based on recommendations in a huge new federal study that shows that dogs are messy and disruptive to natural inhabitants.

That assertion has infuriated dog owners, who are escalating a fight. But the dispute has also raised a larger question: If national parks are for connecting people with nature, then how much does nature need to be protected from us?

“Ninety-nine percent of San Francisco has been destroyed irrevocably,” said Brent Plater, executive director of the Wild Equity Institute, a nonprofit conservation organization that wants dogs to be restricted. “This is really the last space we’ve set aside,” he said of the parks.

In fact, Plater said that the current proposals did not go far enough and that dogs should be limited to fenced-in areas in the parks.

The city of San Francisco is itself a threat to nature, according to Plater. While he does not advocate for the removal of residents and structures, he said several species of local wildlife — including mission blue butterflies and western snowy plovers — were at risk of extinction if dogs’ activities in the parks were not curtailed.

Martha Walters, co-founder of the Crissy Field Dog Group, called such views “environmental extremism” and said nature, people and their pets could coexist.

The debate over dogs in the national recreation area started in 1972 when the United States Department of the Interior began assuming control of the properties. In recognition of the need for public access to nature near San Francisco, the land was designated an urban “recreation area.” And rather than banning dogs off-leash, which is policy at all other national parks, the tradition of allowing dogs to romp free that predated federal management was allowed to continue.

But complaints about unruly dogs and their waste, both from environmentalists and other park visitors, have grown over the years, according to the Park Service. Decades of arguments and lawsuits ensued. At one notorious 2001 public hearing, angry protesters reportedly spit on their foes.

Unable to strike a compromise, the Park Service developed its own dog plan. Almost 2,000 pages long, it makes the case for leashing or banning dogs nearly everywhere. Off-leash play would be allowed in only seven relatively small areas with strict new rules: owners must maintain control and visual contact at all times.

Alexandra Picavet, a spokeswoman for the Park Service, said that despite the recreation area designation, federal law required that “we’re held to the same standards” as other national parks regarding the obligation to preserve nature.

Kenneth S. Weiner, a top environmental lawyer who has been hired by the Crissy Field Dog Group, disagreed. “The law requires some degree of consistency,” Weiner said, “but allows flexibility.”

The proposed rules, which became public in January, are only a draft. Members of the public have until April 14 to offer their opinions online (hundreds of comments have already been submitted) or at a series of public meetings that started this week.

“We will certainly be in a listening mode,” Picavet said.

Experts familiar with the Park Service questioned that assessment and said that in previous cases, the preferences cited in draft reports were almost always adopted, regardless of public opinion.

“The draft concerns us a lot,” said Jennifer Scarlett, a veterinarian and co-president of the San Francisco SPCA. “Dog owners can be the best advocates for the outdoors and the environment.”

Now, Scarlett and other dog owners are determined to persuade the Park Service to change its position. Nearly 300 attended the first public meeting Wednesday at the Tamalpais High School gym in Mill Valley.

An even-larger crowd is expected Saturday at the Seven Hills Conference Center at San Francisco State University beginning at 11 a.m.

Please note: except for service animals, no dogs are allowed. No spitting either.

This article also appears in the Bay Area edition of The New York Times.