BILLINGS, Mont. - Wildlife agencies in the Northern Rockies go to lengths to warn people of the dangers of grizzly country - from signs advising hikers to carry Mace-like bear spray to radio ads that warn hunters to take care when stalking elk in bear habitat.

But after two hikers were fatally mauled in Yellowstone National Park over the summer, officials acknowledge their drive to make visitors "bear aware" is not reaching everyone. As a result, park officials, bear biologists and others say that in coming months they plan to sharpen a bear safety message that was already under review in hopes of preventing future maulings.

"We thought we were doing pretty good," said park biologist Kerry Gunther, pointing to a 30-year average of one bear-caused human injury annually in Yellowstone. "Maybe we were getting lucky."

Many bear education campaigns focus on saving the animals themselves, part of a broader effort to recover a species once nearly wiped out by hunting and other pressures. Slogans such as "a fed bear is a dead bear" highlight the increased likelihood of bears becoming nuisances - and getting euthanized - if they get used to eating human food or garbage.

With the success of the recovery efforts, Yellowstone's grizzly population has now grown to about 600 bears. Those animals are pushing into new areas of Montana, Wyoming and Idaho, where officials also are seeing attacks. There have been about 10 bear encounters that have resulted in human injuries across the region this year, including one Sunday in Grand Teton National Park, officials said. Such incidents have forced agencies to broaden the public safety side of their message.

Also growing is the size of the crowd that message needs to reach: Yellowstone National Park last year hosted a record 3.6 million visitors, and millions more visited five adjacent national forests and nearby Grand Teton National Park.

Among some of those visitors, said University of Wyoming sociology professor Patricia Taylor, "there isn't a real fear of bears or appreciation of how strong they are."

"People will say, 'We want a bear to come to the campground. We want to see it,'" she said.

Both victims of this summer's mauling deaths had visited the park previously. Officials said that indicated they had received at least some exposure to trailhead signs and other information describing how to avoid and respond to bear attacks.

Among the advice commonly offered is to travel in groups, make noise while hiking, carry bear spray - and know how and when to use it.

By contrast, one of the summer mauling victims was alone. Neither was carrying bear spray. And in one case investigators said the victim and his wife may have triggered the attack when they ran, yelling, from an approaching mother grizzly with cubs.

The head of the federal government's grizzly recovery program, Chris Servheen, said that being told what to do around a bear is not enough. Servheen said people in bear country also have to be mentally prepared to take action. He likened that to military training designed to ensure soldiers can react without hesitation to threats, and recommended people conduct practice bear encounter drills so they're comfortable taking out their bear spray, using it if needed and calmly backing away.

Still, nothing can guarantee a safe outcome. A 32-year-old hunter was injured by a bear Sunday afternoon in Grand Teton and, by all accounts, had been following recommendations - including carrying bear spray and dropping to the ground and covering his head. Other details in the attack, including the extent of the hunter's injuries, are not clear.

Both victims in the fatal maulings in Yellowstone fell into the loose category of "day hikers" who might enter the park's backcountry but not camp overnight. However, the most intensive bear safety talks - including instruction on food storage and what to do when charged - are heard by that small percentage of park visitors who spend the night in the wilderness. In 2010, that included slightly more than 45,000 visitors, or just over one percent of the park's total.

Backcountry campers must get a permit and go through what Yellowstone's chief ranger, Tim Reid, described as a rigorous system for teaching them how to have a safe trip. "We're very successful in getting our message across on two of the cardinal rules: food storage and bear awareness and avoidance, and the need to carry bear spray as a preferred deterrent," Reid said.

"Then there's the rest of the world," Reid added - the day hikers. How to reach that much larger group is one focus of the drive to sharpen the region's bear safety message.

Reid suggested it won't be easy. Many of Yellowstone's visitors come from overseas, creating language barriers. Others who pass through the park for only a day or two balk at paying about $50 for a can of bear spray they won't have much use for at home.

The University of Wyoming's Taylor last year surveyed more than 600 Grand Teton visitors to gauge public awareness of bear safety protocols. Most showed at least a basic knowledge of food storage guidelines meant to keep hungry bears away. Almost all correctly answered that running from a bear can trigger aggression in the animal.

Three percent of those surveyed fell into the "clueless" category with no knowledge at all about food storage rules. And more than 12 percent - or about one in eight people - said they knew so much about bears that they could predict when a bruin would turn aggressive.

"That's extraordinary to me," Taylor said. "I'm 60 years old. I've been a backpacker since I was 28 going into backcountry sites. I don't think you can know."