BILLINGS -- The grizzly bear population in and around Glacier National Park is one of the largest in the Lower 48, but for years wildlife officials have only been able to guess at the numbers that support that conclusion. And they can't say whether the population is growing, stable or even in free fall.

Three decades after the bears were listed as a threatened species, the first comprehensive research effort is under way to gather basic information on the size and health of the population. Wildlife officials say knowing this is critical to beginning the long -- and still uncertain -- road to recovery of the species.

''Number alone is not recovery,'' said Chris Servheen, the U.S. Fish and Wildlife Service's grizzly recovery coordinator. ''We've barely started.''

There are two projects in progress. One uses DNA analysis of bear hairs not only to estimate how many bears are out there, but also to learn where they are. The other uses tracking technology to help determine the population trend.

Researcher Kate Kendall, who is leading the DNA project for the U.S. Geological Survey, said about 34,000 bear-hair samples were collected throughout the region from strategically placed wire and locations, such as sign posts, favored by bears for rubbing.

So far, about 460 individual bears have been identified, with a higher concentration in the park, and Kendall expects the minimum count will rise to between 500 and 600 bears once the work is complete. The number of males and females has been running close, with slightly more females so far, she said.

State wildlife officials hope to build off Kendall's work with their tracking efforts. Researchers last year began placing radio collars on female grizzlies, with the goal of evaluating survival and reproduction rates.

Chris Smith, chief of staff for the Montana Department of Fish, Wildlife and Parks, said data gathered from two dozen or so collared bears will be plugged into a computer model to project what the population is doing. But Smith expects it will take at least four years -- and maybe more, depending on tracking and collaring success -- to get a reliable read on whether the population is growing, stable or declining.

This is of particular interest to wildlife officials trying to determine the significance of the high numbers of human-caused grizzly deaths in the Northern Rockies in recent years.

In 2004, 31 grizzlies in northwest Montana were killed by people -- the most since the bears were listed as threatened in 1975. Last year, 25 bears in that region were killed by people, 11 illegally, the greatest number of known illegal kills in recent memory.

''We really haven't been in a good position to determine whether that level of mortality is sustainable or not,'' Smith added.

Of six grizzly recovery zones in the contiguous United States, just two -- the Glacier and Yellowstone ecosystems -- have sizable bear populations of more than a few dozen. While the two have a comparable number of bears, far more is known about the Yellowstone population, which is considered the most studied bear population in the world.

Federal officials last year said they no longer considered Yellowstone-area bears threatened and announced plans to remove the bears from Endangered Species Act protections. A final decision on that is pending.

Once those bears are delisted, Servheen said, his agency's recovery efforts will shift from Yellowstone to other grizzly populations, including those in northwest Montana. ''That's my effort,'' he said. ''I'll be spending more time'' working on those.

Activists wonder about whether there will be the money for the work needed.

''Resources have been a limiting factor, and resources will continue to be a limiting factor,'' said Louisa Willcox of the Natural Resources Defense Council.

Smith said his agency is committed to the bear-tracking effort indefinitely but can only cover about half the cost on its own; the hope is that other agencies will assist, he said.

Servheen said his office has been crippled by a chronic lack of money, and cited that as the reason officials know so little about the Glacier-area bears. Given funding constraints, he said he has no clear answer for how officials might be able to build on what they already have accomplished.