BOULDER, Colo., Nov. 8 - When Greg McCoy found Oreo, his daughter's house cat, in the jaws of a mountain lion early this year, he grabbed the big cat by the tail with both hands, dragged it onto his front lawn and jumped on top of it.

With his left arm, he tried to hold the writhing lion in a headlock. With his right hand, he attempted to yank Oreo from the lion's mouth.

As Mr. McCoy, 37, and 215 pounds, tugged on the bloodied house cat, the lion - an adult female weighing perhaps 100 pounds - struggled out of his headlock. Before it ran off to eat Oreo, it swatted Mr. McCoy across the face with a rear paw.

"It felt like a fist with four nails in it and it brought me to my senses and I decided I better let go," said Mr. McCoy, a founder of a small company that offers wireless broadband Internet access to people who live, as he does, in the mountains on the outskirts of Boulder. "I had read about how to deal with a mountain lion, but none of that entered my head when I saw one with my daughter's cat. I was plain mad stupid."

He was also lucky. The lion left four scratches on his right cheek, which have since healed without leaving scars. Wildlife experts say that swat could easily have torn off much of his face.

These are vexing times for Western suburbanites and the big cats that increasingly skulk among them.

The mountain lion, an ambush predator that was long trapped and poisoned as a varmint, has been resurgent since the 1960's when many Western states categorized it as big game, with limited hunting seasons. No one knows how many there are, but a recent estimate by wildlife ecologists put the number at over 31,000 in 12 Western states.

There may now be more mountain lions in the West than there were before European settlement, said Dr. Maurice Hornocker, a senior scientist at the Wildlife Conservation Society.

"For more than 100 years we kept them away from human development by killing them whenever they showed up," said Dr. Hornocker, who has studied mountain lions for more than 40 years. "That isn't the case anymore, and so they are taking advantage of it. These are highly intelligent and highly adaptive predators."

The human population in states with mountain lions is also surging, with hundreds of thousands of newcomers, like Mr. McCoy, who moved here two years ago from Georgia, choosing to live at the wild edge of suburban sprawl, where cul-de-sacs meld into mountain lion turf.

This mix has coincided with an increase of attacks on people, which now average about four a year, up from one a year before 1970. Since 1890, mountain lions have killed 17 people, 11 of them children, in the United States and Canada. More than half of these deaths, including Colorado's two confirmed fatalities, occurred in the past 12 years.

Now evidence is growing that mountain lions, the world's fourth-largest cat, are moving east, pushed by their own breeding success and pulled by an abundance of deer, their favorite meal, on the far side of the Mississippi.

A car killed a juvenile male last month on Interstate 35 near Kansas City. It was the first confirmed sighting of a free-roaming mountain lion in the region in more than 100 years. Scientists last year confirmed the presence of seven mountain lions in northern Michigan, where the animals were supposedly wiped out 95 years ago.

Using cover along creek and river beds, the cats appear to be exploring east across the Great Plains, with confirmed sightings or roadside carcasses in Nebraska, Kansas, North Dakota, Iowa and Minnesota. Within the past decade, a thriving population has established itself in the Black Hills of South Dakota. Depending on where they live, mountain lions are also called cougars, pumas, panthers and catamounts.

"They will eventually get to New Jersey," or at least close, said Dr. Paul Beier, a professor of wildlife ecology at Northern Arizona University, who has extensively researched mountain lions. "You need them back in the East because you got too many deer," he said. "They are part of a healthy ecosystem."

Scientists have had to revise their understanding of mountain lion behavior since the 1990's, when the rate of human deaths began to spike. Once thought to hunt only at dawn or dusk, the cats began to attack suburban deer in midafternoon. Supposedly averse to humans, a threat only to solitary children, they began to stalk adults and even groups.

One attack in particular shook up the experts, said David H. Baron, an environmental writer who is working on a book, "The Beast in the Garden," about mountain lions in and around Boulder.

In 1991, about 20 miles from here, an 18-year-old man was killed while jogging at midday about 200 yards from a high school.

"This was the attack that wasn't supposed to happen," Mr. Baron said. "This was the first adult to be killed and consumed by a healthy full-grown lion in at least 100 years. Since then, many public officials have been afraid the next death could happen at any time."

Pete Taylor, lead ranger for the Open Space and Mountain Parks Department in Boulder, does not disagree. "I think it is going to happen in town," said Mr. Taylor, who responds to mountain lion sightings in parks and backyards nearly every month. "It took me eight and a half years to see five lions in Boulder. I have seen six in the last 18 months. We are either getting more lions or the lions are getting more used to us."

Still, attacks here and across the West remain rare, much less common than fatal lightning strikes, bee stings or spider bites.

"My question has been `Why don't they hunt people more often?' " said Tina Ruth, a wildlife biologist who has studied mountain lion behavior in Montana, New Mexico, Florida and Texas. "We are a very vulnerable prey item, and we are more and more common in the wild. These animals have an aversion to us as long as they have a viable prey base, but they do rely exclusively on meat."

Experts advise that if people encounter mountain lions they should face them directly, try to appear large, shout and make noise and back away from the animal.

Ms. Ruth, who works for the Wildlife Conservation Society and lives in Montana, says game managers in states east of the Mississippi need to start thinking about whether they want mountain lions moving into their suburbs.

They do get around. Young male mountain lions have been observed traveling 400 miles to establish new territory. Nearly all of these lions, Ms. Ruth said, are forced to find new turf. Those that do not tend to be killed and eaten by their territorial elders.

"With deer available in the East and young cougars heading in that direction, there is going to be an increase in human conflicts," she said. "Now is the time for states to start planning some sort of management strategy, instead of waiting until there is a crisis situation."

To understand what happens when mountain lions are allowed to loiter in the suburbs, there is perhaps no better case study than Boulder, a university town of 96,000 people, many of them young and outdoorsy.

Hugging the foothills of the Rockies and encircled by nearly 100,000 acres of open space, Boulder is open both geographically and as a matter of policy to wildlife that chooses to wander into town.

In the mid-1980's, when 1,000 deer were counted on Boulder's western edge, the City Council voted to let them be, with no hunting or trapping allowed. Many residents seem to feel the same way about the mountain lions that followed the deer into town.

"In Boulder, lions are learning that humans are nothing to be afraid of," Mr. Taylor, the city park ranger, said.

While he added that the city's policy was "to give the cats a negative experience - we carry rubber buckshot to teach them that humans are nothing to mess with" - many residents refuse to report lions because they do not want to get the animals in trouble.

Unlike many other towns in the West, Boulder does not allow rangers to kill lions that eat house pets. "If you are letting your cat or dog run outside, they are fair game," Mr. Taylor said.

Consider the experience of the mountain lion that ate Oreo and swatted Mr. McCoy in the face last January.

Rangers in Boulder will destroy a lion that harms people, but Mr. McCoy did not report the incident.

"I deserved every piece of what happened to me," he said. "We choose to live in their backyard, so we got to put up with them."

With no one to chase her off, that lion continued to hang out in the neighborhood. Two days after wrestling Mr. McCoy, it killed a mule deer behind a house across the street.

Emily Hiller, 9, spotted the visitor. It was breakfasting on bloody flesh in the backyard while she was eating toast with peanut butter in the kitchen. She happened to look out the window. "Oh, it's a mountain lion, mom!" she remembers shouting.

Emily's mother and father, Dottie and Jeffrey Hiller, rushed to the window, took pictures of the cat and invited neighbors over for a look. Mr. McCoy's daughter, Kristina, 9, who is Emily's best friend and whose cat had been killed by the new backyard attraction, was among the visitors. She said she forgave the big cat for eating Oreo.

For nine days, the mountain lion, along with her two cubs, stayed in the Hillers' backyard, calmly eating the deer. No one called animal control authorities.

"It is not every day in your life that you get to have National Geographic outside your window," said Mrs. Hiller, who owns a company that helps people set up offices in their home.

"If we had called animal control, they would have removed her and they would have buckshot her, which is like being beaten with a belt," Mrs. Hiller said.

She said she and her family were concerned that the lion might be separated from "her babies."

The lion's stay in the backyard ended, Mrs. Hiller said, when she noticed it stalking her. She had gone out for groceries and was carrying them into the house when she turned and saw the lion eyeing her through an open garage door. She jumped back in her car and blew the horn. The mountain lion moved on.

Since January, the Hillers and the McCoys say they have been careful not to allow their daughters to walk alone in the neighborhood. Mr. McCoy, though, continues to hike by himself in the woods near his house.

"I don't really fear them," he said.

http://www.nytimes.com/2002/11/12/science/life/12COUG.html